Expandable slide and lock stent

ABSTRACT

An expandable slide and lock stent comprises a tubular member that can be expanded from a collapsed state to an expanded state. The tubular member can comprise a reversing helical backbone and at least one rail member extending from the helical backbone in a circumferential direction. The backbone can have at least one engagement element that can be configured to receive a rail member to form the tubular member. In some embodiments, the reversing helical backbone can comprise a plurality of discrete segments having a variable profile and/or wave form.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims from the benefit of U.S. Provisional ApplicationNo. 61/322,843, filed Apr. 10, 2010, titled “EXPANDABLE SLIDE AND LOCKSTENT,” the entirety of which is incorporated herein by reference.

BACKGROUND

1. Field

The present disclosures relate generally to expandable medical implantsfor maintaining support of a body lumen, and more specifically, to auniform stent having improved mechanical and post-deployment dynamiccapabilities.

2. Description of the Related Art

Various embodiments of vascular implants; such as stents, thrombusfilters, and heart valves, are used in their various embodiments formedical applications. Of these vascular devices, one of the leadingcandidates as a stent device and structural component is the radiallyexpandable and slidably engaged stent as disclosed in commonly ownedU.S. Pat. Nos. 6,033,436; 6,224,626; and 6,623,521; the disclosures ofwhich are hereby incorporated by reference in their entirety. Theseradially expandable and slidably engaged stents offer the strength ofprior expandable stents with the added improvements of low cross-sectiondeliverability, less bulk material thickness, high resolution fitting,and shape customization such as hourglass-shape configurations.

Other radially expandable and slidably engaged stents; such as thosedisclosed in U.S. Pat. Nos. 5,797,951; 5,549,662; and 5,733,328; furtherdescribe the state of the art and their disclosures are herebyincorporated by reference.

Although promising candidates for use as implantable devices and devicecomponents, these known radially expandable and slidably engaged stentshave mechanical and vasodynamic limitations of which the inventors ofthe present application set out to address. These limitations can becharacterized as deployment related limitations, and limitations relatedto vasodynamic capabilities.

Deployment related limitations of prior art stents are herein described.Intravascular space; especially that of a patient in need of a vascularimplant, is generally inconsistent and varies upon the individual withrespect to curvature, plaque buildup and other luminary obstructions.Furthermore, the shape and structure of the stent may impact the rateand order that discrete areas of the stent deploy, e.g., expand. Forinstance, one portion of the stent may expand prior to a second portionof the stent. Such inconsistent and/or non-uniform deployment may renderdeployment and placement of prior art stents more difficult and lesspredictable.

Procedures are available to physicians such as balloon angioplasty,which aid in the reduction of plaque prior to stenting. However, evenafter such procedures, vascular characteristics remain patientdelineated and largely inconsistent. Inconsistencies in vascularcharacteristics; such as the interference due to a luminary occlusion,require flexibility, distribution of material strength, and vascularadaptability of devices to be implanted.

SUMMARY

In accordance with at least one of the embodiments disclosed herein is arealization that the configuration of a vascular implant, such as astent, affects the deployment characteristics of the implant. Forexample, the shape and structure of the stent may impact the rate andorder that discrete areas of the stent deploy, e.g., expand. Forinstance, based at least in part on the characteristics of the stent,one portion of the stent may expand prior to a second portion of thestent. In some embodiments, the stent can be designed withcharacteristics such that the stent advantageously deploys substantiallyequally along a longitudinal length of the stent. Accordingly, variousembodiments disclosed herein provide a stent that can be deployed orexpanded in a generally uniform manner without binding.

Further, in accordance with at least some embodiments disclosed hereinis the realization that a helical stent can often experience binding ordeployment problems as the helical arrangement unwinds, which must occurfrom either or both ends of the helical stent. As a result, expansion inthe center of the helical stent delayed until the helix is “unwound”from its ends. These expansion characteristics are unsatisfactory asthey provide nonuniform deployment and structural properties.Accordingly, in order to address these deficiencies, the inventors ofthe present application have developed various embodiments of areversing helical stent having a reversing helical backbone thatadvantageously provides vastly improved deployment and structuralcharacteristics. Further details such embodiments are provided herein,and can incorporate various features, structures, materialconfigurations, and other attributes such as those disclosed in thecopending U.S. patent application Ser. No. 12/577,018, filed Oct. 9,2009, titled “EXPANDABLE SLIDE AND LOCK STENT,” the entirety of which isincorporated herein by reference.

Further, in accordance with some embodiments is the realization that theshape and structure of a stent can impact whether the stent undergoes atwisting or rotation about a longitudinal axis of the stent duringdeployment. In certain instances, it can be advantageous to reduce orminimize the twisting of a stent during expansion, e.g., to facilitateexpansion of the stent by reducing friction between components of thestent and/or between the stent and the vasculature. For example, thestent can include a longitudinally-extending structure (e.g., a backboneor backbone member) that can extend at least partially (e.g. helically)around a circumference of the stent. In some cases, such a configurationcan promote deployment, provide torsional flexibility, and reducetwisting of the stent. As disclosed herein, embodiments are disclosedherein that enable such a configuration to not only provide portableflexibility, but to also provide reduced binding of the stent duringdeployment.

In accordance with some embodiments, the stent can comprise at least onebackbone coupled with at least one rail member. The backbone cangenerally extend along a longitudinal axis of the stent. The rail membercan generally extend in a circumferential direction of the stent. Thus,the rail member can define a portion of a circumference of the tubularmember. Generally, the rail member can be configured to permit one-waysliding movement of the backbone relative to the rail member so as topermit expansion of the tubular member from the collapsed state to theexpanded state.

The backbone can extend helically about the tubular member. In someembodiments, the backbone can comprise a reversing helical shape orconfiguration. A “reversing helical” shape can be defined as one thatchanges its circumferential direction as it extends in an axialdirection. In some embodiments, a path of a reversing helical backbonecan extend helically about the tubular member in a first axial directionand a first circumferential direction and change its path to a secondcircumferential direction. For example, changing course from the firstto the second circumferential direction can include changing from aclockwise circumstantial direction to a counterclockwise circumferentialdirection. However, these are compression direction can also be variedin only the counterclockwise or clockwise circumferential directions.

In some embodiments, the reversing helical backbone can define one ormore elbows or points where the direction or path of the backbonechanges. Further, the shape of the backbone can also define at least onepeak or high point and at least one trough or low point. For example,when seen from a side view, the backbone can extend in a generallyupward direction having an overall positive slope until reaching a peakor uppermost point. Likewise, the backbone can extend from the peak in agenerally downward direction having an overall negative slope untilreaching a trough or lowermost point. In some embodiments, the shape ofthe backbone can comprise a plurality of peaks and troughs. Thus, thereversing helical shape can be characterized as comprising an undulatingshape, a zig-zag shape, a wave pattern, a sinusoidal shape, and/or thelike. Surprisingly, such a configuration can promote deployment of thestent. Additionally, such a configuration can allow for stentcharacteristics to be modified and/or selected for the requirements of aparticular application, e.g., rate of expansion of the stent, force toexpand the stent, etc.

Additionally, in some embodiments, at least some of the peaks and/orvalleys of the backbone of the stent can be pointed or sharply angled,e.g. a sawtooth, triangle, or the like. In some embodiments, at leastsome of the peaks and/or valleys of the backbone of the stent can becurved, smoothed, rounded, chamfered, filleted, or the like. Further, insome embodiments, some of the peaks and valleys of the backbone can bepointed while others are rounded. In some embodiments, a generallyrounded or smooth curve at a peak or valley can promote an overallrounded shape of the stent. Further, a generally pointed peak or valleymay promote a desired strength, flexibility or rigidity characteristic.Thus, some embodiments of the stent can be configured to createlocalized stiffness, strength, flexibility, patency, roundness, and/orother characteristics by manipulating the shape of peaks and valleys andthe angular direction of the backbone, as discussed further herein. Forexample, a rounded peak may reduce the tendency for the peak to protrudeinto the lumen of the stent. Thus such a feature can assist inmaintaining the patency of the lumen.

In accordance with some embodiments, the reversing helical backbone canbe curvilinear (e.g. having a reversing curvilinear shape). For example,the reversing helical backbone can comprise one or more continuouscurves, one or more smooth curves, a continuously variable curvature,and/or the like. In some instances, the reversing helical backbone canbe formed in an undulating reversing helical configuration. For example,the reversing helical configuration can extend generally in a wavepattern, a sawtooth pattern, a triangular pattern, a rectangularpattern, a zig-zag pattern, and/or the like. Further, the backbone canextend in a regular, repeating, and/or symmetrical pattern. However, inother embodiments of the stent, the backbone can extend in an irregular,non-repeating, and/or asymmetrical pattern.

Accordingly, the reversing helical configuration of the backbone cancomprise nearly any wave form. For example, the reversing helicalconfiguration can have a substantially constant amplitude. The amplitudeis the distance between the adjacent peak and valley, as measuredperpendicular to a longitudinal axis of the backbone. In otherembodiments, the reversing helical configuration can have asubstantially non-constant, varying, or changing amplitude.

Furthermore, in some embodiments, the reversing helical configurationcan have a substantially constant period. The period is the distance orinterval between adjacent peaks or adjacent valleys, as measuredparallel to the longitudinal axis of the backbone. In other embodiments,the reversing helical configuration of the backbone can have asubstantially non-constant, varying, or changing period. In some cases,the period can include one peak and one valley. In some embodiments, theperiod can include two peaks and one valley. In some embodiments, theperiod includes two valleys and one peak. In some cases, the period mayspan the entire length of the stent.

In accordance with at least some embodiments disclosed herein is therealization that the angular direction of the longitudinally-extendingbackbone structure can affect the characteristics of the stent. Forexample, a shallower angle (in relation to the longitudinal axis of thestent) can ease deployment of the stent. Conversely, a steeper angle (inrelation to the longitudinal axis of the stent) can provide enhancedlongitudinal flexibility of the stent and/or radial strength of thestent. As discussed further herein, surprising and advantageous resultsregarding the flexibility and deployment characteristics of a stent havebeen achieved by the inventors of the present application throughimplementing stent configurations disclosed herein. In particular,outstanding results have been obtained through implementing stentconfigurations having a reversing helical backbone with smooth orcurvilinear peaks and valleys and a series of short-phase angledeviations along the length of the backbone between consecutive peaksand valleys.

Furthermore, in some embodiments, the reversing helical configurationcan be defined as comprising a plurality of short-phase or leg elements.For example, in a backbone having a sinusoidal reversing helicalconfiguration, each portion of the sinusoid from a valley toward a peakcan be a short-phase or leg element, and each portion of the sinusoidfrom a peak toward a valley can be a short-phase or leg element.Generally, adjacent leg elements can have opposite slopes, e.g., a legelement with a positive slope will normally follow a leg element with anegative slope, and vice-versa.

In some embodiments, one or more of the short-phase or leg elements canbe generally straight, generally curvilinear, or define a sub-pattern orvariable shape configuration. For example, in some embodiments one ormore of the leg elements can itself comprise a wave pattern, a sawtoothpattern, a triangular pattern, a rectangular pattern, a zig-zag pattern,and/or the like. Thus, in some cases, the backbone can have a reversinghelical configuration and one or more of the leg elements can have apattern that deviates from a generally straight length. In particular,some embodiments of the stent can provide a sinusoidal reversing helicalbackbone having a wave sub-pattern that extends between the peaks andtroughs of the sinusoidal reversing helical backbone.

In some embodiments, the amplitude of the sub-pattern or variable shapeof the leg elements is less than the amplitude of the reversing helicalbackbone. Surprisingly, the use of a sub-pattern on a reversing helicalbackbone has been found to advantageously promote uniform deployment ofthe stent. For example, it has been found that such a pattern-on-patternconfiguration can reduce twisting and/or promote deployment of thestent. Furthermore, such a configuration can also exhibit the advantageof allowing stent characteristics to be modified and/or selected for therequirements of a particular application, e.g., rate of expansion of thestent, force to expand the stent, etc. For example, localizedcharacteristics of the stent can be designed for given results, whichprovides substantial advantages and customization ability for thestents.

Furthermore, the inventors have also determined that embodiments of thereversing helical stents disclosed herein can also advantageously permitthe implementation of longer stents that were not possible with certainprior art stents. Such prior art stents exhibited a “critical length”because their length was limited due to the expansion force requirementsof the stent and the expansion force limitations of the catheterballoon. Above a certain size, some balloons were not strong enough toproperly deploy such stents. In particular, a helical stent might createundue stress on the balloon toward the center of the stent due to thebinding problems discussed above. However, embodiments of the reversinghelical stent discussed herein can equalize the expansive force requiredto deploy the stent and avoid localized binding (and the additionalforce needed thereat) to expand the stent. Thus, embodiments of thereversing helical stent disclosed herein do not have the same criticallength limitations as other helical stents.

Although many of the structural features discussed herein may be shownand described with reference to the circumferential orientation of thestent, some of the features and advantages provided by the reversinghelical configuration can be implemented in the width dimension of thestent (e.g., along the radial direction of the stent). In some cases,the reversing helical configuration can be present in the thicknessdimension of the backbone (e.g., in a radial dimension of the stent).Some embodiments can have a reversing helical configuration in the widthand thickness dimensions of the backbone.

It is also contemplated that embodiments disclosed herein can reduce orminimize the twisting of a stent during expansion. Reducing orminimizing twisting can, for example, reduce friction between componentsof the stent and/or between the stent and the vasculature. In someinstances, a reversing helical configuration can reduce binding of thestent during deployment by, for example, decreasing the relative motionof different components of the stent during expansion. For example, thereversing helical configuration can reduce the rotation of one end ofthe stent during expansion, from the vantage of a second end of thestent.

A further realization in accordance with at least one of the embodimentsdisclosed herein is that the configuration of the stent can impact thedeployed shape of the stent. In some embodiments it may be desirable forthe deployed stent to be substantially round, e.g., circular incross-section. A substantially round stent can facilitate, for example,improvement of stent strength and placement of the stent in thevasculature. In at least one of the embodiments disclosed herein, astent can include features to facilitate a substantially round shape inthe deployed state. The stent can include one or more components, suchas a longitudinally-extending structure (e.g., a backbone), thatpromotes the roundness of the stent. For example, the backbone can beshaped substantially as a sinusoid. In particular, at least one peak ofthe sinusoidal backbone is curved, e.g., not formed as a pointed peak orhaving a sharp angle. Such a rounded peak can promote an overall roundedshape or roundness of the stent. For example, the rounded peak canreduce the tendency for the peak to protrude into the lumen of thestent.

In some embodiments, surprising results have been found in furtherpromoting roundness by implementing configurations in which the railmembers are selectively oriented in opposing circumferential directions.For example, some embodiments, a first rail member can extendcircumferentially in a first direction and a second rail member canextend circumferentially in a second direction. In some arrangements,the direction in which the first and second rail members extend can berelated to or dependent upon the angle between the rail member andlongitudinally-extending structure. For example, in some cases, thefirst and second rail members extend in a given circumferentialdirection such that the angle between the rail member andlongitudinally-extending backbone or structure is an acute angle.Accordingly, it has been determined that, compared to stents with otherfeatures, e.g., non-reversing structures, a reversing helical backbonecan promote roundness of the stent.

In some embodiments, the backbone can comprise one or more engagementelements. The engagement element can comprise a slot, indentation,passageway, aperture, protrusion, and/or other such structures. In manyembodiments illustrated herein, the engagement element comprises a slotthat can be configured to receive corresponding rail members, whichextend along the circumferential axis of the stent. In some cases, theslots and/or rail members have a locking mechanism configured to permitonly one-way sliding movement of the rail members with respect to theslots. In some cases, the locking mechanism can comprise one or moreteeth, ridges, paddles, detents, ratchets, ramps, hooks, stops, and/orthe like.

In some embodiments, the slots can be angled with respect to thelongitudinal axis of the stent, which can advantageously effect thecharacteristics of the stent. For example, a shallower angle (inrelation to the longitudinal axis of the stent) can decrease the forcerequired to expand the stent, and thus can ease deployment of the stent.A steeper angle (in relation to the longitudinal axis of the stent) canincrease the longitudinal flexibility of the stent and/or radialstrength of the stent, and thus provide a stronger yet more flexiblestent.

In some cases, the slot angle can be determined at least in part by theposition of the slot along the aforementioned reversing helicalconfigurations of the backbone and/or the leg element. For example,positioning the slot on a more steeply angled portion of reversinghelical configurations can generally produce a steeper slot angle.Conversely, positioning the slot on a more shallowly angled portion ofreversing helical configurations can generally produce a shallower slotangle.

The slot can be disposed at an angle that is different from the angle ofthe leg element overall (relative to the longitudinal axis of thestent). For example, in some cases a leg element is angled at about 10°to about 45° from the longitudinal axis of the stent, and the slot isangled at about 5° to about 60° from the longitudinal axis of the stent.In some embodiments, the absolute value of the slot angle can be betweenat least about 0 degrees and/or less than or equal to about 60 degrees.The absolute value of the slot angle can also be between at least about10 degrees and/or less than or equal to about 50 degrees. Further, theabsolute value of the slot angle can be between at least about 20degrees and/or less than or equal to about 40 degrees. The slot anglecan also vary between at least about 30 degrees and/or less than orequal to about 35 degrees. Finally, as illustrated, the absolute valueof the slot angle can be approximately 10 degrees, 33 degrees, 40degrees. Further, it is contemplated that the slot angle can be anyvariety or combination of desired angles that are configured tofacilitate ease of expansion on the one hand and stent flexibility onthe other hand.

In embodiments with multiple slots, each slot can be disposed at anangle that is different than the angle of adjacent slots. For example,in an embodiment with three slots, the first slot can be angled at afirst angle, the second slot can be angled at a second angle, and thethird slot can be angled at a third angle, wherein the first, second,and third angles are not equal.

Generally, each slot angle can be selected. Advantageously, in light ofthe above-discussed realization that different angles of the stentcomponents can impact stent characteristics, employing slot angles thatare selectable allows the stent to be customized for specificapplications. For example, in applications in which radial strengthand/or longitudinal flexibility are desired, the steeper slot angles canbe employed; in applications in which ease of expansion is desired,shallower slot angles can be employed. Beneficially, it has been foundthat a stent having a combination of steep and shallow slot angles canprovide a balance of radial strength, longitudinal flexibility, and easeof expansion.

As discussed above, the tubular member can include one or more railmembers that are slidably coupled to a backbone and define a portion ofthe circumference of the tubular member. The term “rail member” canrefer to on or more elongate, circumferentially extending rails thatinterconnect with at least one backbone the stent. The rail members insome embodiments can be coupled to or formed with an adjacent railmember to form a radial element. For example, the radial element can begenerally U-shaped with a pair of rail members extending therefrom. Someembodiments can include a plurality of adjacent rail members or radialelements that interconnect with one or more respective backbones.Further, groups of rail members and/or radial elements can becircumferentially associated to form a circumferential band or radialmodule. In some arrangements, each radial element within a radial modulecan be coupled to a different backbone. For example, in an embodimentwith a radial module having first and second radial elements, the firstradial element can be coupled to a first backbone and the second radialelement can be coupled to a second backbone.

In some arrangements, each radial element within a radial module can beslidingly engaged with an engagement element of a different backbone. Insome embodiments, the engagement element can comprise a slot, a passage,a channel, and/or aperture extending through or along a backbone. Forexample, in an embodiment with a radial module having first and secondradial elements, the first radial element can be slidingly received inan engagement element in a second backbone and a second radial elementcan be slidingly received in an engagement element in a first backbone.Of course, other numbers and combinations of radial elements andbackbones are contemplated, e.g., one, three, four, etc. As previouslydiscussed, the radial element and/or the slot can be configured toprovide one-way sliding movement of the radial element with respect tothe engagement element.

A further realization in accordance with at least one of the embodimentsdisclosed herein is that a modular stent can advantageously permit agiven stent design provide multiple stent lengths. In such a design, theoverall length of the stent can be increased or decreased by adding orsubtracting modules. As similarly noted above, the modules can provide acircumferential and corresponding axial length to the stent. Further,the axial length of a module can correspond to the periodicity of thebackbone, whether having a reversing helical or regular helicalconfiguration. Thus, modular construction can refer to the use of one ormore modules or sections that may be used to build the entire length ofthe stent. Modular construction generally also allows for addition andsubtraction of the modules or sections in order to reach a desired size.Further, longitudinal modules or sections, including a backbone andcorresponding rail members or radial elements, can also added or removedto a stent construction in order to modify the maximum and minimumdiameters of the stent. Thus, a stent with a modular construction canadvantageously be modified (by adding or subtracting longitudinal orcircumferential sections or modules) to provide, for example, a desiredexpanded diameter or length. For example, additional backbones can beadded to the stent to provide an increased expanded diameter. Further,additional radial modules or sections can be added to provide a longerstent (which would require increasing the length of the backbone andproviding additional rail members or radial elements correspondingthereto).

In some embodiments, an expandable slide and lock stent is provided inwhich the stent comprises a tubular member having a circumference and alongitudinal axis. The stent can comprise a first backbone and a secondbackbone and at least one rail member. The first and the secondbackbones can each have a reversing helical shape. The first and secondbackbones can extend along at least a portion of the circumference andalong the longitudinal axis. In some embodiments, the first and secondbackbones can be reversing helical backbones defining a generallycurvilinear sub-form extending along the backbones between a peak and avalley of the reversing helical backbones.

In some embodiments, at least one of the first and second backbones candefine one or more discrete segments. The discrete segments can comprisethat portion of the backbone extending between engagement elements ofthe backbone. Further, the discrete segments can also comprise theportion of the backbone at which the engagement elements are positioned.Furthermore, a backbone can be divided into two or more, and in someembodiments, four or more discrete segments. The number of discretesegments can be even or odd, as long as the overall path of the backboneachieves a desired angular orientation, flexibility profile, andstrength characteristics.

The discrete segments can define a discrete helix angle. The discretehelix angle can be a general measurement of the angular direction of thediscrete segment relative to the longitudinal axis of the stent. In someembodiments, one or more of the discrete segments of the backbone candefine a discrete helix angle that is the same as or different from thediscrete helix angle of another discrete segment. Further, in someembodiments, the discrete helix angle can be referred to as a slot anglemeasured at an engagement element or slot of the backbone.

Furthermore, some embodiments can be configured such that one or more ofthe discrete segments are generally curvilinear. The curvilinear shapecan have increasingly positive slope, a decreasingly positive slope,increasingly negative slope, or a decreasingly negative slope. Thus, incontrast to straight or pointed portions of a backbone, the curvilineardiscrete segments can provide improved flexibility, bending strength,and roundness of the stent.

The rail member can define proximal and distal ends. The proximal end ofthe rail member can be coupled to the first backbone. The distal end ofthe rail member can extend from the first backbone in thecircumferential direction. The rail member can be configured to engagewith an engagement element in the second backbone. Further, the railmember can be configured to provide one-way movement of the secondbackbone away from the first backbone such that the tubular member canbe expanded between a collapsed diameter and an expanded diameter.

The reversing helical shape of the backbones can comprise a reversingundulating shape. The reversing helical shape can comprise a portionhaving a positively trending slope and a portion having a negativelytrending slope. At least one of the portions having a positivelytrending slope and the portion having a negatively trending slope canfurther comprise a plurality of wave forms. The plurality of wave formscan comprise a plurality of continuous curves. Further, the intersectionof the rail member and the second backbone can be at an oblique angle.

The stent can further comprising a plurality of rail members definingproximal and distal ends. The proximal end of each of the rail memberscan be coupled to the first backbone. The distal end of each of the railmembers can extend from the first backbone in the circumferentialdirection and can be configured to intersect and pass through one of aplurality of slots in the second backbone.

Further, one or more of the slots in the backbone can define a slotangle that extends skew relative to the longitudinal axis of the stent.For example, these slot angles of the slots in the backbone can bedifferent from each other, as discussed further herein. For example, insome embodiments, each of the slot angles can be disposed at a differentangle with respect to the longitudinal axis compared to adjacent slotangles. Further, the slot angles can also be generally equal to eachother.

In some embodiments, the rail member can comprise one or more teeth forengaging the slot to provide one-way expansion of the stent.Accordingly, and some embodiments, the slot can comprise a centralpassage and at least one internal recess for engaging the teeth of therail member.

In accordance with another embodiment, methods for forming the standsand stent components are provided. For example, any of the embodimentsdisclosed herein can be formed by initially forming the structuresdisclosed, such as the reversing helical backbone, the discrete segments(depending on their configuration), and the like. For example, a methodfor forming a stent can be provided which comprises: forming a centralpassage as a first through hole in the backbone in a circumferentialdirection of stent, and forming the at least one internal recess as asecond through hole in the backbone in a direction transverse to acircumferential direction of the central passage such that the first andsecond through holes partially overlap.

Next, in accordance with some embodiments, an expandable stent isprovided that can comprise a plurality of radial componentsinterconnected to form a tubular member. The stent can comprise at leastone reversing helical backbone having a plurality of slots and furthercomprising a plurality of rail members. The reversing helical backbonecan define a generally curvilinear sub-form extending along the backbonebetween a peak and a valley of the reversing helical backbone. Further,the rail members can be received into the slots of the helical supportmember to facilitate one-way expansion of the stent. The expandablestent can be made from a bioresorbable polymer. Further, these stent canbe configured to exhibit structural properties equivalent to a metalstent.

Furthermore, a radial structure, module or element for forming anexpandable slide and lock polymer stent can be provided which comprisesan undulating helical backbone and a plurality of the elongate ribbedelements. The undulating helical backbone can half a plurality ofengagement slots and a plurality of connection slots. The at least oneengagement slot can be spaced between consecutive connection slots alongthe backbone. The plurality of elongate rib elements can have proximaland distal portions. The proximal portion can be interconnectable withone or more connections slots of the continuously slotted backbone. Eachrib element can be positionable generally circumferentially about thelongitudinal axis and have a fixed engagement at a nonperpendicularangle with respect to the helical backbone.

The plurality of elongate rib elements can be arranged to interconnectwith at least one other undulating helical backbone of another radialelement so as to form an expandable tubular skeleton. The elongate ribelements can have a one-way slidable engagement with the engagementslots of the helical backbone of the other radial element. The tubularskeleton can be configured to expand radially between a collapseddiameter and an expanded diameter upon circumferential motion of theslidable engagement of the rib elements to the helical backbones.Further, the slidable engagement can include a mechanism restrainingcollapse of the tubular skeleton from the expanded diameter towards thecollapsed diameter.

In some embodiments, the undulating helical backbone can compriseportions of reduced thickness for allowing at least partial nesting ofan elongate rib element thereagainst. Further, a pair of elongate ribelements can be interconnected at their distal portions by a crossbar.The crossbar can comprise an offset portion configured to at leastpartially receive an elongate rib of an adjacent radial element forreducing a passing profile of a stent formed using a plurality of radialelements. Next, the undulating helical backbone can extend helically ata generally fixed radius and helix angle relative to the longitudinalaxis. The engagement slot can comprise a through slot that defines acentral axis extending in a generally circumferential direction andwithin a plane that is perpendicular to the longitudinal axis of theradial element, the central axis of the engagement slot can extend at anon-perpendicular angle relative to the helical backbone.

BRIEF DESCRIPTION OF THE DRAWINGS

The abovementioned and other features of the embodiments disclosedherein are described below with reference to the drawings of theembodiments. The illustrated embodiments are intended to illustrate, butnot to limit the embodiments. The drawings contain the followingfigures:

FIGS. 1 and 2 show planar representations of two embodiments of a stentor stent assembly, illustrating different interconnecting arrangementsof the backbones and radial elements.

FIG. 3 shows an assembly in which rail members of the radial elementsare generally obliquely oriented with respect to the stent longitudinalaxis, and perpendicular to the backbones, according to an embodiment.

FIGS. 4A and 4B show a stent assembly with backbones arrayed generallyin an slanted or helical orientation, having portion which is parallelto the stent axis, according to an embodiment.

FIG. 5 shows a stent assembly with multiple locally non-slanted backboneportions, according to an embodiment.

FIGS. 6, 7, and 8 each show embodiments of stent assemblies in which thebackbones have bi-directional, multidirectional or continuously variablebackbone orientation along the stent longitudinal axis, according to anembodiment.

FIGS. 9A-9D illustrate an embodiment with multi-directional rail memberarrays, in expanded and collapsed configurations.

FIGS. 10A-10F illustrate alternative embodiments in which the teeth orlocking members are provided with one or more relieving holes orindentions located within the rail member, according to an embodiment.

FIGS. 11A-11D illustrate the engagement of teeth or locking members onthe rail members of the radial element, according to an embodiment.

FIG. 12A illustrates a stent embodiment having rail modules with railmembers, in the compacted state, according to an embodiment.

FIG. 12B illustrates the stent embodiment of FIG. 12A in the expandedstate, according to an embodiment.

FIG. 13A illustrates an end view of the stent embodiment of FIG. 12A ina tubular configuration, according to an embodiment.

FIG. 13B illustrates an end view of the stent embodiment of FIG. 12B inthe tubular configuration, according to an embodiment.

FIG. 14A illustrates a perspective view of the stent embodiment of FIG.12A in the tubular configuration, according to an embodiment.

FIG. 14B illustrates a flexed or bent configuration of the stentembodiment of FIG. 12A in the tubular configuration, as potentiallydeployed in a curving vascular lumen, according to an embodiment.

FIGS. 15A and 15B schematically illustrate the relation of backbones torail members, according to an embodiment.

FIG. 16 illustrates a detail of a mid portion of the stent assembly ofFIG. 12A, according to an embodiment.

FIG. 17A illustrates a plan view of an embodiment of a backbone of thestent embodiment of FIG. 12A, according to an embodiment.

FIG. 17B illustrates an elevation view of an embodiment of a backbone ofthe stent embodiment of FIG. 12A, according to an embodiment.

FIG. 17C illustrates a focused view of a portion of the stent embodimentof FIG. 17A, according to an embodiment.

FIGS. 17D and 17E illustrate focused views of a slot of the stentembodiment of FIG. 17B, according to an embodiment.

FIG. 18 illustrates a radial element having a pre-formed shape,according to an embodiment.

FIGS. 19A-19B illustrate embodiments of a backbone having a pre-formedshape, according to an embodiment.

FIGS. 20A-20D illustrate an assembly process of mounting embodiments ofrail members to an embodiments of backbone, according to an embodiment.

DETAILED DESCRIPTION

As will be discussed herein, embodiments of the stent summarized aboveand defined by the enumerated claims may be better understood byreferring to the following detailed description, which should be read inconjunction with the accompanying drawings. This detailed description ofembodiments, set out below to enable one having skill in the art tobuild and use one particular implementation, is not intended to limitthe enumerated claims, but to serve as a particular example thereof.While the description sets forth various embodiments in specific detail,it will be appreciated that the description is illustrative only andshould not be construed in any way as limiting the same. Furthermore,various applications of the embodiments, and modifications thereto,which can occur to those who are skilled in the art, are alsoencompassed by the general concepts described herein.

Overview

As discussed herein, in accordance with at least one of the embodimentsdisclosed herein is the realization that a vascular implant mayexperience a number of mechanical limitations related to delivery. Forexample, some portions of the vasculature are curved or substantiallynon-cylindrical. These portions of the vasculature have proven difficultto deploy stent devices. Sometimes, the curvature of the vessel cancause a deployed stent to fold, especially in stents with insufficientflexibility in the design. Curved vessels further increase the potentialfor hinging and denting as described in further detail below.

A vascular implant may also experience a number of countering forcespost-deployment. Some of these countering forces are a result of what isherein referred to as vasodynamics; the resulting movements,constrictions and contortions of the vasculature. Of these counteringforces is crush force, caused by post-expansion elastic recoil of thevessel.

Additionally, some stents experience an occlusion-derived impactionforce; a point force derived from the impact of a luminary occlusiondirectly onto the device; such a luminary occlusion can be plaque or athrombus. Other countering forces such as dilation, and contortion, areto be discussed in further detail below.

In accordance with an aspect of at least some embodiments is therealization that known radially expandable and slidably engaged stentscan experience what the inventors of this application refer to herein as“hinging.” Many slidably-engaged expandable stents possess a commonlimitation where the engagements are generally longitudinally aligned,thereby inherently creating an alignment of failure points. A failurepoint is a weakness in a stent design, usually a point where two partsare joined together in a less than permanent fashion such as anengagement between slidably-engaged rail members and/or radial modules.When an amount of radial pressure is exerted on the expanded stent, thestent tends to buckle or fold at the failure point. A series of failurepoints that are longitudinally aligned can act as a perforation in thematerial and cause a substantial weakness and propensity for hinging.

Another plaque-related problem is herein referred to as “denting.”Denting is caused by an inherent device pattern weakness where avaso-occlusion can drive a portion of at least one stent module into theluminary space, thereby substantially enhancing the effect of thevaso-occlusion. Such an occlusion or dent can lead to collection ofthrombus or flow distortions which are problematic and can increasestenosis.

Vascular plaque is typically non-uniform and often forms in a bulkyocclusion, such an occlusion can place added stress on the stent via apoint force, and increase the risk of hinging or denting.

The inventors of the present application have recognized that dentingcan significantly dampen or interfere with vasodynamics, and thereforemay cause an increase in realized stenosis. Furthermore, denting may notbe immediately apparent to the implanting physician where a polymerstent is adapted for increased ductility over time.

In accordance with at least one of the embodiments disclosed herein is arealization that the configuration of a vascular implant, such as astent, may effect the deployment characteristics of the implant. Forexample, the shape and structure of the stent may impact the rate andorder that discrete areas of the stent deploy, e.g., expand. Forinstance, based at least in part on the characteristics of the stent,one portion of the stent may expand prior to a second portion of thestent. In some embodiments, the stent can be designed withcharacteristics such that the stent advantageously deploys substantiallyequally along a longitudinal length of the stent. Accordingly, variousembodiments disclosed herein provide a stent that can be deployed orexpanded in a generally uniform manner without binding.

In accordance with some embodiments disclosed herein, the stent can beslidably expandable. The geometry of the stent may be generallydescribed as a tubular member. The tubular member can have a collapsedstate and an expanded state.

Many devices are fabricated from a biodegradable polymer which maybecome substantially more ductile and flexible with the progression oftime up to a point of water absorption equilibrium. As water isabsorbed, the polymer material becomes bendable or ductile. Differingpolymer compositions will have a varied rate of moisture absorption. Theinventors of the present application recognized the benefits ofcontrolled water absorption into the polymer material such as a reducedpropensity for microfissures. Furthermore, the inventors of the presentapplication recognized detriments such as a propensity for denting wherethe design pattern provides unsupported adjacent components. Thelikelihood of denting occurrences is increased for stent patternslacking the support of a structural backbone, especially when there areunsecured corners or other points having a propensity for weakness.Often, the extent to which denting occurs cannot be determined untilseveral hours after the deployment procedure, hence the importance tominimize the potential for denting and improving the design pattern ofthe target device.

In accordance with at least one of the embodiments disclosed herein, theinventors of the present application have recognized that amechanically-improved stent design will overcome one or more of thelimitations set out above, and will further set out to increaseadaptability to the dynamics of the vasculature.

Many prior art stent embodiments are designed around crush force andmaintaining patency of a luminary space. Although patency of the lumenis of primary concern, there are other factors which must be addressedin an effort to go beyond functionality, but rather to move toward thesuccessful treatment and healing of a vessel.

The vasculature is a dynamic system. Although it is difficult toquantify, the vasculature may experience a number of dynamic movementsat any given moment in time. Of these is a wave-like dilation, whichpresents variability in the interior diameter of the vessel at a givenlocation. Dilation can occur from a change in blood pressure or otherchange in the circulation. Additionally, portions of the vasculature canexperience a contortion or twist like motion in addition to dilation.Where there is plaque or a luminary occlusion, the vasculature canexperience a resistance to these natural movements. Such a resistancecan cause the adjacent tissue to undergo a cytotic response, such as thedivision of cells, or intravascular cell growth known as neointimalgrowth. Neointimal growth is a new or thickened layer of arterial intimaformed especially on a prosthesis or in atherosclerosis by migration andproliferation of cells.

Clinical data generally shows that stent implants stimulate neointimalgrowth in the vessel immediately subsequent to implantation. Neointimalgrowth is acceptable up to a point where blood pressure is substantiallyincreased or where the lumen is obstructed and blood can no longerefficiently pass.

It is thought that resistance to vasodynamics, among other things, candramatically increase stenosis surrounding an implanted vascular device.Therefore, it is critical to understand the dynamics of the vasculatureand to design a stent capable of maintaining patency of the lumen whilepromoting the motions associated with vasodynamics such as periodicdilation and contortion. A stent designed to incorporate the dynamics ofthe vasculature can better serve to treat and ultimately heal thevessel.

Generally, neointimal growth surrounds and encompasses the implantedstent, leaving the stent to reside substantially within the new vesselwall. It is in this state that stent mechanics are critical inminimizing further stenosis.

Although stents can be made of generally any biocompatible material,there is a movement toward the use of stents fabricated from abiodegradable and bioresorbable polymer. Biodegradation is thestructural decomposition of a polymer, often occurring as bulk erosion,surface erosion, or a combination thereof. Bioresorption includes thecellular metabolism of the degraded polymer. The inventors of thepresent application have set out to design a stent capable of utilizingthe degradation and resorption properties of the polymer to enhance thehealing and treatment of the vessel.

In some embodiments, there is provided a stent having a uniformdistribution of failure points. This uniform distribution can minimize,if not eliminate the potential for hinging and denting. Further, in someembodiments, there is provided a stent having a rotationally flexiblebackbone capable of adaption to vasodynamic movements, therebyminimizing stenosis of the vasculature.

In some embodiments, there is provided a stent design capable of beingefficiently encapsulated with neointimal growth, such that initialdegradation of the stent material will transform the stent into arotationally flexible and vaso-adaptive support within the new vesselwall.

In summary, there remains a need for an improved radially expandable andslidably engaged luminary support structure: one that uniformlydistributes failure points about the device so as to prevent hinging,one that provides adequate support to components so as to preventdenting, one that embraces the effects of water absorption so as toprevent micro fissures while providing effective stenting to thevasculature, one that is capable of restoring vaso-motion to the treatedvessel upon neo-intima containment, and one that embraces knownproperties of radially expandable and slidably engaged supportstructures such as low cross-section deliverability, less bulk materialthickness, high resolution fitting, and shape customization such ashourglass-shape configurations.

An expandable stent is disclosed in accordance with an embodiment of thepresent inventions. The stent can provide radial support to maintainpatency of a lumen, a flexible vaso-adaptive backbone structure, and auniform circumferential distribution of slidable engagements.

Aside from radial expansion and an ability to maintain patency of thebody lumen, the present disclosure provides solutions to theaforementioned problems of hinging, denting and restriction ofvasodynamic movements.

In accordance with at least one of the embodiments disclosed herein isthe realization that a propensity for hinging is increased in stentdesigns having an alignment of engagement means that are substantiallyparallel with respect to the longitudinal axis of the stent. Further, inaccordance with at least one of the embodiments disclosed herein is therealization that a potential for denting can be minimized byincorporating a support backbone to secure the extremities and cornersof those members or features associated with maintaining patency of thelumen, herein elongate members.

Additionally, in accordance with at least one of the embodimentsdisclosed herein is the realization of the importance of providing astent having flexibility sufficient to promote and adapt to naturalvasodynamic movements while maintaining patency of the lumen. Further,stenosis can be minimized by improving the flexibility of the stent soas to provide adaption to vasodynamic movements such as wave-likedilation and contortion movements.

The term “stent” is used herein to designate embodiments for placementin (1) vascular body lumens (i.e., arteries and/or veins) such ascoronary vessels, neurovascular vessels and peripheral vessels forinstance renal, iliac, femoral, popliteal, subclavian and carotid; andin (2) nonvascular body lumens such as those treated currently i.e.,digestive lumens (e.g., gastrointestinal, duodenum and esophagus,biliary ducts), respiratory lumens (e.g., tracheal and bronchial), andurinary lumens (e.g., urethra); (3) additionally such embodiments can beuseful in lumens of other body systems such as the reproductive,endocrine, hematopoietic and/or the integumentary,musculoskeletal/orthopedic and nervous systems (including auditory andophthalmic applications); and, (4) finally, stent embodiments can beuseful for expanding an obstructed lumen and for inducing an obstruction(e.g., as in the case of aneurysms).

The term “stent” is further used herein to designate embodiments suchas; support structures for maintaining patency of a body lumen; supportstructures for anchoring thrombus filters and heart valves; as well assupport structures for the distribution and delivery of therapeuticagents as well as other devices.

In the following description of embodiments, the term “stent” can beused interchangeably with the term “prosthesis” and should beinterpreted broadly to include a wide variety of devices configured forsupporting a segment of a body passageway.

Furthermore, it should be understood that the term “body passageway”encompasses any lumen or duct within a body, such as those describedherein.

Still further, it should be understood that the term “shape-memorymaterial” is a broad term that can include a variety of known shapememory alloys, such as nickel-titanium alloys, as well as any othermaterials that return to a previously defined shape after undergoingsubstantial plastic deformation.

The term “radial strength,” as used herein, describes the externalpressure that a stent is able to withstand without incurring clinicallysignificant damage. Due to their high radial strength, balloonexpandable stents are commonly used in the coronary arteries to ensurepatency of the vessel. During deployment in a body lumen, the inflationof the balloon can be regulated for expanding the stent to a particulardesired diameter. Accordingly, balloon expandable stents can be used inapplications wherein precise placement and sizing are important. Balloonexpandable stents can be used for direct stenting applications, wherethere is no pre-dilation of the vessel before stent deployment, or inprosthetic applications, following a pre-dilation procedure (e.g.,balloon angioplasty). During direct stenting, the expansion of theinflatable balloon dilates the vessel while also expanding the stent.

General Stent Geometry

In accordance with the principles disclosed herein, the geometry of thestent may be generally described as a tubular member. The tubular membercan be expanded from a collapsed state to an expanded state.

In accordance with these various features, the slidably engagedexpandable stent can include at least one backbone or backbone membercoupled with at least one rail member, elongate member or radialelement. As discussed herein, a plurality of rail members (also referredto as elongate members or rails), such as two or more, can be coupledtogether to form a radial element. The backbone and the rail memberand/or radial element can define a circumference of the tubular member.Generally, the rail member is configured to permit one-way slidingmovement of at least one of the backbones (in relation to the railmember), so as to permit expansion of the tubular member from thecollapsed state to the expanded state.

In some embodiments, the stent can comprise one or more reversinghelical backbones. Many of the reversing helical backbones of theembodiments described herein provides a high degree of longitudinalstructural integrity combined with longitudinal flexibility and radialstrength, both in the compacted and deployed configurations. One or moreelongate members, elongate rails, or radial elements can extend from thebackbone and can interlock with one or more other backbones to form aninterwoven circumferential surface that provides crush strength andradial stiffness without unduly inhibiting longitudinal or rotationalflexibility. In some embodiments, the generally circumferentialalignment of the radial elements allows the elongate members to engageeach other and the backbone in a configuration which provides“hoop-strength,” thus providing a substantial increase overalllongitudinal “beam” stiffness. In some embodiments, the generallycircumferential alignment of the radial elements allows the elongatemembers to engage each other and the backbone without direct coupling ina configuration to provide “hoop-strength” and a substantial increaseoverall longitudinal “beam” stiffness. In certain embodiments, the stentstructure may be described as expandable tubular “skeleton” assemblydefined by the systematic movable interconnection of a pluralityreversing helical “backbones” via a plurality of circumferentiallyarranged rail or “rib” elements.

In some embodiments, the backbone comprises one or a plurality ofengagement elements. The engagement element can comprise a slot,indentation, passageway, aperture, protrusion, and/or other suchstructures. In many embodiments illustrated herein, the engagementelement comprises at least one slot. In other words, embodiments of thebackbone can be configured to comprise one or a series of slots formedalong the backbone for facilitating interconnection of the backboneassembly with one or more rail members or radial elements. This may bereferred to as a continuously slotted backbone. The slots of thebackbone can be advantageous by reducing the tendency for hinging,kinking, and buckling of the stent. Indeed, in some cases, the slots inthe backbone can provide for local areas of reduced stiffness and/orenhances flexibility. Further, in conjunction with the unique reversinghelical backbone structure and slide-and-lock expansion mechanism ofembodiments disclosed herein, the slotted backbone can also contributeto superior flexion and crush strength of the stent.

Generally, the backbone comprises a reversing helical shape, such as ashape that has an alternating positive and negative slope. For example,the reversing helical shape can be a zig-zag, undulation, wave pattern,or the like. In some cases, the reversing helical shape is curvilinearor a series of continuous curves, smooth curves, continuous variablecurvature, or the like. In some arrangements, the reversing helicalshape is symmetrical along the longitudinal axis of the stent. Forexample, in some embodiments the backbone comprises a sinusoidal shape.

As discussed above, a “reversing helical” shape can be defined as onethat changes its circumferential direction as it extends in an axialdirection. In some embodiments, a path of a reversing helical backbonecan extend helically about the tubular member in a first axial directionand a first circumferential direction and change its path to a secondcircumferential direction. For example, changing course from the firstto the second circumferential direction can include changing from aclockwise circumstantial direction to a counterclockwise circumferentialdirection. However, these are compression direction can also be variedin only the counterclockwise or clockwise circumferential directions.

In some embodiments, the reversing helical backbone can define one ormore elbows or points where the direction or path of the backbonechanges. Further, the shape of the backbone can also define at least onepeak or high point and at least one trough or low point. For example,when seen from a side view, the backbone can extend in a generallyupward direction having an overall positive slope until reaching a peakor uppermost point. Likewise, the backbone can extend from the peak in agenerally downward direction having an overall negative slope untilreaching a trough or lowermost point. In some embodiments, the shape ofthe backbone can comprise a plurality of peaks and troughs. Thus, thereversing helical shape can be characterized as comprising an undulatingshape, a zig-zag shape, a wave pattern, a sinusoidal shape, and/or thelike. Surprisingly, such a configuration can promote deployment of thestent. Additionally, such a configuration can allow for stentcharacteristics to be modified and/or selected for the requirements of aparticular application, e.g., rate of expansion of the stent, force toexpand the stent, etc.

Additionally, in some embodiments, at least some of the peaks and/orvalleys of the backbone of the stent can be pointed or sharply angled,e.g. a sawtooth, triangle, or the like. In some embodiments, at leastsome of the peaks and/or valleys of the backbone of the stent can becurved, smoothed, rounded, chamfered, filleted, or the like. Further, insome embodiments, some of the peaks and valleys of the backbone can bepointed while others are rounded. In some embodiments, a generallyrounded or smooth curve at a peak or valley can promote an overallrounded shape of the stent. Further, a generally pointed peak or valleymay promote a desired strength, flexibility or rigidity characteristic.Thus, some embodiments of the stent can be configured to createlocalized stiffness, strength, flexibility, patency, roundness, and/orother characteristics by manipulating the shape of peaks and valleys andthe angular direction of the backbone, as discussed further herein. Forexample, a rounded peak may reduce the tendency for the peak to protrudeinto the lumen of the stent. Thus such a feature can assist inmaintaining the patency of the lumen.

In accordance with some embodiments, the reversing helical backbone canbe curvilinear. For example, the reversing helical backbone can compriseone or more continuous curves, one or more smooth curves, a continuouslyvariable curvature, and/or the like. In some instances, the reversinghelical backbone can be formed in an undulating reversing helicalconfiguration. For example, the reversing helical configuration canextend generally in a wave pattern, a sawtooth pattern, a triangularpattern, a rectangular pattern, a zig-zag pattern, and/or the like.Further, the backbone can extend in a regular, repeating, and/orsymmetrical pattern. However, in other embodiments of the stent, thebackbone can extend in an irregular, non-repeating, and/or asymmetricalpattern.

Accordingly, the reversing helical configuration of the backbone cancomprise nearly any wave form. For example, the reversing helicalconfiguration can have a substantially constant amplitude. The amplitudeis the distance between the adjacent peak and valley, as measuredperpendicular to a longitudinal axis of the backbone. In otherembodiments, the reversing helical configuration can have asubstantially non-constant, varying, or changing amplitude.

Furthermore, in some embodiments, the reversing helical configurationcan have a substantially constant period. The period is the distance orinterval between adjacent peaks or adjacent valleys, as measuredparallel to the longitudinal axis of the backbone. In other embodiments,the reversing helical configuration of the backbone can have asubstantially non-constant, varying, or changing period. In some cases,the period can include one peak and one valley. In some embodiments, theperiod can include two peaks and one valley. In some embodiments, theperiod includes two valleys and one peak. In some cases, the period mayspan the entire length of the stent.

In accordance with at least some embodiments disclosed herein is therealization that the angular direction of the longitudinally-extendingbackbone structure can affect the characteristics of the stent. Forexample, a shallower angle (in relation to the longitudinal axis of thestent) can ease deployment of the stent. Conversely, a steeper angle (inrelation to the longitudinal axis of the stent) can provide enhancedlongitudinal flexibility of the stent and/or radial strength of thestent. As discussed further herein, surprising and advantageous resultsregarding the flexibility and deployment characteristics of a stent havebeen achieved by the inventors of the present application throughimplementing stent configurations disclosed herein. In particular,outstanding results have been obtained through implementing stentconfigurations having a reversing helical backbone with smooth orcurvilinear peaks and valleys and a series of short-phase angledeviations along the length of the backbone between consecutive peaksand valleys.

Furthermore, in some embodiments, the reversing helical configurationcan be defined as comprising a plurality of short-phase or leg elements.For example, in a backbone having a sinusoidal reversing helicalconfiguration, each portion of the sinusoid from a valley toward a peakcan be a short-phase or leg element, and each portion of the sinusoidfrom a peak toward a valley can be a short-phase or leg element.Generally, adjacent leg elements can have opposite slopes, e.g., a legelement with a positive slope will normally follow a leg element with anegative slope, and vice-versa.

In some embodiments, one or more of the short-phase or leg elements canbe generally straight, generally curvilinear, or define a sub-pattern orvariable shape configuration. For example, in some embodiments one ormore of the leg elements can itself comprise a wave pattern, a sawtoothpattern, a triangular pattern, a rectangular pattern, a zig-zag pattern,and/or the like. Thus, in some cases, the backbone can have a reversinghelical configuration and one or more of the leg elements can have apattern that deviates from a generally straight length. In particular,some embodiments of the stent can provide a sinusoidal reversing helicalbackbone having a wave sub-pattern that extends between the peaks andtroughs of the sinusoidal reversing helical backbone.

In some embodiments, the amplitude of the sub-pattern or variable shapeof the leg elements is less than the amplitude of the reversing helicalbackbone. Surprisingly, the use of a sub-pattern on a reversing helicalbackbone has been found to advantageously promote uniform deployment ofthe stent. For example, it has been found that such a pattern-on-patternconfiguration can reduce twisting and/or promote deployment of thestent. Furthermore, such a configuration can also exhibit the advantageof allowing stent characteristics to be modified and/or selected for therequirements of a particular application, e.g., rate of expansion of thestent, force to expand the stent, etc. For example, localizedcharacteristics of the stent can be designed for given results, whichprovides substantial advantages and customization ability for thestents.

Various embodiments described herein can provide for a polymeric stentthat exhibits advantageous structural properties that are comparable tothose of a metal stent. For example, research has illustrated that thehelical backbone construction, paired with the slide-and-lockinterconnection of radial elements, can be used in a polymer stent suchthat the advantages of bioresorbability and superior structuralstiffness and strength (similar to that of a metal stent) can berealized. This significant advance in stent technology allows otherpreferable materials—not just metals—to be used in a stent to achievedesirable material properties, while ensuring that the necessarystructural properties of the stent are also achieved.

The slidably engaged radial elements can be configured forunidirectional slidable movement so as to permit the radial expansion ofthe tubular member. In an embodiment, the stent can define a firstcollapsed diameter, and a second expanded diameter. The slidably engagedexpandable stent is adapted to be expandable between at least the firstcollapsed diameter and at least the second expanded diameter.

In some embodiments, the slidably engaged expandable stent is configuredwith two radial modules, each radial module being slidably engaged andconfigured for unidirectional expansive movement. Each radial module caninclude a backbone, a first elongate member and a second elongatemember. In some embodiments, the elongate members are annular elongatemembers; in some embodiments, the elongate members are ring-like memberselongated from the backbone. The elongate members can be slidablyengaged with slots and can be configured for unidirectional slidablemovement.

The slidably engaged expandable stent in some embodiments has aplurality of radial elements, including a first radial element and asecond radial element. These radial elements can be substantiallycommonly oriented with respect to the backbone. The second radialelement can be axially or circumferentially offset with respect to thefirst radial element.

The axially or circumferential offsetting of rail members and/or radialelements allows a distribution of slidable engagements. Such adistribution of slidable engagements is said to render the stent uniformwith respect to mechanical failure points; as the slidable engagementsare generally the weakest mechanical points in the design. Slidableengagements are herein defined as the engagement means between twoslidably engaged radial modules. In some embodiments, the slidableengagements are defined by the interlocking of slots and contained railmembers of the slidably engaged radial elements.

The slots can further comprise a locking member. A locking member canbe, for example, a tooth, a deflectable tooth, stop, ridge, paddle,detent, ratchet, ramp, hook, or the like. In some embodiments, the slotscomprise a number of stops inside the surface or cavity of the slot. Inanother embodiment, the slots comprise at least one tooth adjacent tothe entry side of the slot.

The slots can be angled with respect to the longitudinal axis of thestent, which can to provide further advantages to the stent. Forexample, it has been determined that a shallower angle (in relation tothe longitudinal axis of the stent) can decrease the force required toexpand the stent, and thus can ease deployment of the stent. A steeperangle (in relation to the longitudinal axis of the stent) can increasethe longitudinal flexibility of the stent and/or radial strength of thestent, and thus provide a stronger yet more flexible stent. Thus,appropriate slot angles may be selected to promote desired stentcharacteristics.

Additionally, the elongate members can be configured to comprise atleast one conjugate locking member. A conjugate locking member isessentially a component designed to engage with the locking member. Insome embodiments, a conjugate locking member is adapted to fit beengaged by the locking member. In one embodiment, the conjugate lockingmember is one of a tooth, a deflectable tooth, or a stop. A lockingmember and a conjugate locking member define an engagement means wherebythe radial elements, rail members, and/or radial modules are slidablyengaged. Exemplary conjugate locking members are described in co-pendingU.S. patent application Ser. No. 12/577,018, filed Oct. 9, 2009, titled“EXPANDABLE SLIDE AND LOCK STENT,” the entirety of which is incorporatedherein by reference.

The backbone can comprise a flexible link, such as a spring link.Alternatively, the flexible backbone can be made of an elastomericpolymer material sufficient to promote adaption to vasodynamicmovements. Elastomeric polymers are defined in the art, however forillustrative purposes examples can include polycaprolactone,polydioxanone, and polyhexamethylcarbonate.

Various embodiments of the stents disclosed herein can incorporatevarious features, structures, material configurations, and otherattributes of Applicant's patents and co-pending patent applications,such as U.S. patent application Ser. Nos. 11/016,269, 11/455,986,11/196,800, 12/193,673, 11/399,136, 11/627,898, 11/897,235, 11/950,351,11/580,645, 11/680,532, and U.S. Pat. No. 6,951,053, each of which arehereby incorporated by reference in their entireties.

EXAMPLES

FIGS. 1-20D illustrate examples of stent embodiments having aspects ofthe embodiments disclosed herein. For clarity of the stent structure,certain of these figures illustrate various stent embodiments in a flat(e.g., unrolled) state. It should be understood, however, that such fordelivery and/or implantation in a vascular structure, such embodimentscan be rolled to form a tubular member. Although parts of the stent mayhave been illustrated as being on opposite sides of the stent (see,e.g., FIG. 9A, elements 732 a and 735) for clarity, in the rolled statesuch elements can be slidingly engaged (see, e.g., FIG. 9C). Variousfigures include a representation of a longitudinal axis 640 of a stentif formed into a tubular member. The longitudinal axis 640 can provide aframe of reference in measuring relative angles and orientations ofcomponents of the stents disclosed herein. However, the longitudinalaxis 640 may not in all figures represent a center axis of the stent,but instead represent an axis extending parallel to a center axis of thestent.

Cross-Over Rail Pattern Versus Discrete Rail Modules

FIGS. 1 and 2 show planar representations of the circumferentialsurfaces (in the tubular state) of embodiments of a stent or stentassembly. The examples of FIGS. 1 and 2 illustrate two differentinterconnecting arrangements of the elongate members or rail members ofthe stents, which extend generally circumferentially so as to integratethe stent assembly. The embodiments illustrated have generally U-shapedrail elements and three backbones. Other embodiments have more or fewerthan three backbones. In other embodiments, the rail members need not beU-shaped, e.g., alternative shapes, such as “W-shaped” members and thelike, may be advantageously employed).

FIG. 1 shows a stent assembly 650 with 3 backbones 652 a-c. Theplurality of rail members or rail elements 654 are arranged in tripletpatterns bonded to respective adjacent backbones. In this arrangement,cutting lines AA, BB and CC can be seen to cross all three backboneswithout intersecting any rail member. In this sense, the rail membersmay be described as being arranged in distinct radial modules. Theradial modules may contain more or fewer than three rail members.

Further, in some embodiments, rail members or radial elements of acircumferentially extending radial module can be positioned adjacent toor at least partially overlap with rail members or radial elements ofanother circumferentially extending radial module. The spacing oroverlap of adjacent radial modules can promote stiffness and flexibilityof the stent.

For example, in the assembled tubular stent is illustrated in FIG. 1, aseparation between distinct radial modules can promote a relative degreeof flexibility at these junctions (the regions of cutting lines AA, BBand CC).

Further, FIG. 2 shows an assembly 660 with a plurality of backbones 662a-c. The plurality of rail members 664 are arranged in an overallcross-over pattern with respect to adjacent rail members. In thisarrangements, cutting lines A′A′ and B′B′ can be seen to necessarilycross one or more rail members in traversing the array of backbones. Inthis sense, the rail members may be described as being integrated in across-over or partial overlap arrangement, without distinct or separatedradial modules. As discussed above, in the assembled tubular stent, sucha cross-over arrangement can promote radial strength and continuityalong the axis of the stent.

As with other embodiments of this disclosure, the concepts illustratedin FIGS. 1 and 2 may be used in combination. For example, one or moreportions of the stent length may have a crossover pattern (e.g., arobust center section adjacent a lesion or plaque being supportedradially), while other portions may be arranged as distinct modules(e.g., distal and proximal terminal modules suited to flexing to vesselcontours).

Rail Pattern Perpendicular to Helical or Slanted Backbones

While many of the examples described herein have patterns of railmembers oriented generally perpendicular relative to the stentlongitudinal axis 640 (and generally obliquely oriented with respect tothe helical or slanted portions of the backbones), alternativearrangements may be employed without departing from the unique and novelaspects disclosed herein.

For example, FIG. 3 shows an assembly 670 with three backbones 672 a-c,arrayed generally parallel with one another, and set at an anglerelative to the stent longitudinal axis 640. The rail elements 674,however, are generally aligned perpendicular to the backbones 672 a-c.As may be seen in Arrow 677, the direction of sliding of the toothedportion of the rail member 674 with respect to the backbone pass-throughslot is at an angle to the stent axis.

Note that in FIG. 3, as well as in several of the figures beginning withFIG. 1, the elements of the stent assembly may be shown in an untrimmedor unfinished configuration, with portions 676 a of the rail membersextending outward beyond the bonding slots of the backbone. Theseportions are provided for manufacturing convenience during assembly andthe bonding and/or affixing of rail elongate portions to backbonestructure. The extended portions may be trimmed to final shape 676 b byknown methods (blades, laser cutting, and the like) during the finalassembly process. Similarly, in many of the figures, an extendedproximal and distal portions of backbones is shown, which may be trimmedto a final desired length as a manufacturing procedure.

Non-Slanted Backbone Portions

It is often desirable to have the stent deploy or expand within a lumenin a uniform manner along its axis. In other cases, it may be desired tohave portions of the stent deploy before or later than others. Aballoon-based deployment system may tend to apply greater force orpressure at certain points along the stent axis, or inflate sooner atdifferent longitudinal points. The stent structure may be tailored toachieve the desired deployment sequence.

In at least some deployment scenarios it may be advantageous, at certainlongitudinal portions of the stent backbones, to have less mechanicalresistance to expansion of the rail members through the pass-throughengagement elements, than at other longitudinal portions. For example,where a balloon catheter deployment system tends to inflate more readilyin the center than at the terminal ends, it may be advantageous tocompensate for this by having less resistance to expansion of theterminal portions of the stent (or one end) than in a center portion.Thus, in some arrangements the stent can advantageously be configured tomitigate non-uniform expansion of the balloon catheter, e.g., the stentcan be configured to expand substantially uniformly although the ballooncatheter expands non-uniformly.

FIGS. 4A and 4B show a stent assembly 680 with three backbones 682 a-c,arrayed generally parallel to one another in an locally slanted orhelical orientation. FIG. 4B is a detail of the upper-left corner ofFIG. 4A. Rail members 684 are arranged bonded to the backbones andpassing though slots in adjacent backbones. However, one or more of thebackbones (e.g., all three in the example illustrated) may have aportion 685 which is less slanted or generally parallel to the stentaxis. This less slanted or generally parallel portion 685 can facilitatemotion of the rail elongate elements 684 through the pass through slotsbeing generally parallel to the backbone at the un-slanted portion 686a, and generally oblique to the backbone at slanted portion 686 b.

In certain cases, in an assembly of generally helically aligned orslanted backbones, a short section of backbone parallel to the axis ofthe stent at a terminal end of the stent cab enhance radial rigidity ofthe stent, particularly where the terminal end is supported by the lastrail in sequence of the array, such as the left-hand portion of 682 a.Thus a non-slanted terminal backbone portion may be advantageouslyincluded one or more of the backbones of a stent assembly, e.g., stentassembly 680.

FIG. 5 shows a stent assembly 690 with three backbones 692 a-c arrayedgenerally parallel to one another in a generally slanted or helicalorientation. Similar to the example shown in FIGS. 4A and 4B, one ormore of the backbones 692 a-c can include multiple portions that arelocally non-slanted or less-slanted (e.g., generally parallel to thestent longitudinal axis 640). In FIG. 5, several of these portions aremarked with circles. For example, in some embodiments, one or more ofthe left end, right end, and/or a middle portion of at least one of thebackbone 692 a-c can contain such a non-slanted or less-slanted portion.In the particular example illustrated in FIG. 5, each backbone has threespaced-apart non-slanted portions. As shown, rail pass-through slotportions 696 a can be provided with a perpendicular backbone-rail memberalignment where the backbone portion is non-slanted. In this manner thedeployment characteristics of the assembly may be tailored along thelongitudinal axis of the stent, while maintaining an overall slanted orhelical backbone pattern.

Bi-Directional, Multi-Directional or Variable-Directional BackboneArrays

While many of the examples described have patterns of backbones orientedgenerally helical array, generally at a consistent angle to the stentlongitudinal axis, alternative arrangements may be employed withoutdeparting from the unique and novel aspects disclosed herein.

In the example assembly 700 shown in FIG. 6, each backbone 702 a-c has aslant angle that reverses at the mid-portion of the assembly. As shown,some embodiments can further include a medial non-slanted portion. Asnoted above, the inventors have noted that a “non-reversing” helicalstent tends to unwind from either end toward the center, which createsbinding and increased resistance to expansion in the center of thestent. Surprisingly, the inventors have determined that creating a stentwith a reversing helical backbone and positioning the peak or apex ofthe reversing helical backbone at about the midpoint of the stent canreduce the tendency of the stent to bind during expansion.

However, by implementing the reversing helix illustrated in FIG. 6, theinventors have surprisingly determined that deployment of the stent canbe more uniform and that binding is reduced in the center of the stent.In solving this problem, the inventors have also noted that a decreasedamount of binding attributable to the helical arrangement takes place atapproximately the one-quarter and three-quarter marks of the stent—thepoints between the ends and the center point where the helix reverses.Accordingly, as discussed further herein, the inventors have inventednew and unique solutions for reducing and/or eliminating binding of thestent in these and other areas where localized binding may build.

In the example assembly 710 shown in FIG. 7, each backbone 712 a-cincludes a curvilinear portion and defines has a slant angle or slope(with respect to the stent axis) that is continuously variable fromproximal end to distal end. This continuously variable curve extendingbetween respective peaks and valleys of the backbones can providesuperior flexibility and deployment characteristics, as discussedherein. In the illustrated embodiment of FIG. 7, the slope changes fromnegative to positive (as viewed from left to right in the figure) at thevalleys of the backbones or midpoint of the assembly, giving thebackbone an overall cosine wave appearance in this illustration. Therounded apex of the cosine wave can inhibit the apex from protrudinginto the lumen when the stent is in the rolled configuration. Avoidingsuch protrusions can be advantageous at least for the reason that suchprotrusions can block flow through a portion of the lumen. Additionally,inhibiting the apex from protruding into the lumen, can facilitate anoverall round shape of the stent, as discussed above. Further, comparedto a stent having a sharply angled peak (which could become entangledwith or even puncture vasculature or the catheter balloon) the roundedapex of the cosine wave can generally slide against vasculature or thecatheter balloon, thus facilitating delivery and deployment of the stentassembly.

Like the example of FIG. 7, in the example assembly 720 shown in FIG. 8,each backbone 722 a-c includes a curvilinear portion and also has aslant angle or slope (with respect to the stent axis) that iscontinuously variable from proximal end to distal end. In theillustrated embodiment, the slope changes from positive to negative (asviewed from left to right in the figure) at the peaks of the backbonesor midpoint of the assembly, giving the backbone an overall sine waveappearance in this illustration. As discussed above, the rounded apex ofthe wave can inhibit the apex from protruding into the lumen of thestent, can promote a more round overall stent shape, and can avoidentanglement during delivery and deployment. Further, as shown, in somecases a trident or W-shaped rail member 714 b or 724 b can be providedat the apex of the sine or cosine shape or enhancing flexibility andstrength of stent at the peaks or valleys of the backbones.

In the examples of FIGS. 7 and 8, the backbone array provides a smoothtransition between portions that are minimally sloped and portions thatare markedly sloped. Many of the other embodiments illustrated in theappended figures provide similar advantages.

The absolute value of the overall helix angle (the angle at which abackbone extends relative to the longitudinal axis 640 of the stent) ofthe backbones of embodiments of the stent can be between at least about15 degrees and/or less than or equal to about 60 degrees. The absolutevalue of the overall helix angle of the backbones can also be between atleast about 20 degrees and/or less than or equal to about 50 degrees.Further, the absolute value of the overall helix angle of the backbonescan be between at least about 22 degrees and/or less than or equal toabout 30 degrees. In some embodiments, the absolute value of the overallhelix angle of the backbones can be about 25 degrees.

Bi-Directional or Multi-Directional Rail Member Arrays

While many of the examples described have patterns of rail members orradial elements oriented in a consistent direction from proximal todistal end of the array, alternative arrangements may be employedwithout departing from the unique and novel aspects disclosed herein.

FIGS. 9A-9D illustrate an embodiment that provides an improved deployedshape of the stent. In some embodiments it may be desirable for thedeployed stent to be substantially round, e.g., circular incross-section. The illustrated embodiment includes one or morecomponents, such as a longitudinally-extending structure (e.g., abackbone) and a unique rail member arrangement that promotes theroundness of the stent. In some embodiments, excellent results forfurther promoting stent roundness have been found by implementingconfigurations in which rail members are selectively oriented inopposing circumferential directions.

For example, some embodiments, a first rail member can extendcircumferentially in a first direction and a second rail member canextend circumferentially in a second direction. In the example assembly730 shown in FIGS. 9A-9D, the direction of orientation of arrays of therail members or radial elements is reversed at the peaks of thebackbones or at a midpoint of the stent assembly. In this particularexample, the backbones 732 a-c are arrayed similarly to the example ofFIGS. 7 and 8, e.g., each backbone 732 a-c is generally curvilinear andhas a slant angle or slope with respect to the stent axis that changesdirection of slope in the middle portion. Thus, the backbones can bedescribed as reversing helical backbones having smooth or curved peaksand valleys.

With respect to the peaks or middle portion of the backbone array (shownin the expanded position in FIG. 9A and in the collapsed position inFIG. 9B), the rail members 734 are oriented with cross-members 735 ofthe U or W shaped rail members extending “upward” (in the drawing), andthus extending to the “outside” of the adjacent backbone curvature 732a. With respect to the left and right end portions of the backbonearray, the rail members are oriented with cross-members 735 of the railmembers 734 extending “downward” (in the drawing), and thus alsoextending to the “outside” of the adjacent backbone curvature 732 c.

In the illustrated embodiment, as in the embodiment of FIGS. 1 and 2,the middle portion of the rail member array is a distinct radial modulefrom the end portions. In other words, the embodiment illustrated inFIG. 9A illustrates three radial modules that are spaced apart from eachother and provide, in a tubular member, independent circumferentialmodules. However, within the middle portion, the rail members form acrossover arrangement. Accordingly, as discussed above, in such anembodiment the middle portion can include enhanced radial strength andcontinuity along the axis of the stent, while the end portions can haveenhanced flexibility to flex to vessel contours.

In some arrangements, the direction in which the first and second railmembers extend can be related to or dependent upon the angle between therail member and longitudinally-extending structure. For example, in somecases, the first and second rail members extend in a givencircumferential direction such that the angle between the rail memberand longitudinally-extending backbone or structure is an acute angle.Accordingly, it has been determined that, compared to stents with otherfeatures, e.g., non-reversing structures, a reversing helical backbonecan promote roundness of the stent.

As shown, the backbone can be shaped substantially as a sinusoid. Inparticular, at least one peak of the sinusoidal backbone can be curved,e.g., not formed as a pointed peak or having a sharp angle. Such arounded peak can further promote an overall rounded shape or roundnessof the stent. For example, the rounded peak can reduce the tendency forthe peak to protrude into the lumen of the stent.

Enhanced Tooth Deflection and Resiliency

FIGS. 10A-10F illustrate alternative embodiments of the teeth or lockingmembers provided on the elongate elements or rails of the variousembodiments shown herein for engaging with the backbones in or adjacentthe pass-through slots. Each of FIGS. 10A-10F shows a portion of rail774 including a plurality of teeth 772. In some embodiments, the teethare positioned on multiple edges of each elongate element. In otherembodiments, the teeth are on positioned a single edge, such as is shownin FIGS. 10A-10F.

The embodiments shown the FIGS. 10A-10F each have one or more relievingopenings 776 located within the rail member, which can reduce stressconcentrations as the teeth 772 are deflected as they pass through theslot during stent expansion. In some cases, the relieving openings 776may decrease force needed to deflect the teeth 772. Advantageously, therelieving opening 776 can also promote stiffness of the tooth in theopposite direction, thus enhancing the one-way ratcheting configurationof the stent. Further, such relieving openings 776 can allow for ashallower configuration of the teeth to be employed, thus promotingmanufacturability and reducing the amount of material than is removed toform the teeth 772.

Such relieving openings 776 may extend through the material of the rail744 (open holes) or may only extend partially through the material onone or both sides (indentations). The relieving openings 776 may, forexample, prevent or reduce stresses in the teeth 772 during deploymentso as to avoid or reduce plastic deformation, and to increase theeffective rebound of the tooth as it passes beyond the pass-through slotof the backbone.

Note that the teeth 772 need not necessarily have a toothlikeappearance, and alternative profiles may be employed, as shown in FIGS.10E and 10F. In these embodiments, the locking portion is rounded, anddepresses inward under the forces of deployment.

FIGS. 11A-11D show the action of engagement teeth or locking membersprovided on the elongate elements or rails of the rail members,configured for engagement with slots in the backbones of the stentembodiments described herein. In some respects, the example shown isparticularly similar to the locking mechanism depicted in theembodiments of FIGS. 12A-14B, discussed below. In the example of FIGS.11A-11D, the rail member 770 includes a pair of elongate rails 773 a and773 b (note: there may be more than two, e.g., see member 724 b in FIG.8).

A reference frame for the rail member 770 may be defined relative to thebackbone to which it is to be fixedly mounted, joined or bonded in theassembled stent. In this reference frame, each of rails 773 a-b ofmember 770 has a proximal end 772 a-b configured to be fixedly mountedor bonded to a supporting backbone (e.g., 782 a in FIG. 12A). In thisreference frame, the rail elements 773 a-b, as assembled, will extenddistally to engage a sliding slot 787 of an adjacent backbone (e.g., 782b in FIG. 12A). Each of rails 773 a-b includes a medial portion 774 a-bsupporting a locking mechanism 776 a-b. In the illustrated embodiment,the locking mechanism 776 is disposed on only one side of rail 773.Other embodiments have at least some of the locking mechanism 776disposed on both sides of the rail 773 a and/or 773 b. The rails 773 aand 773 b are joined at their distal ends by cross-member 775. Inalternative embodiments, where member 770 has more than two rails,cross-member 775 may join more than two rails.

In the detail drawing FIG. 11B, it may be seen that the lockingmechanism 776 comprises a sequential plurality of locking elements 777,which are illustrated as being tooth-like in this example. The lockingelements 777 can be separated by indented connecting regions 778. Insome cases, at least one stress management or relieving opening 779 isdisposed adjacent connecting regions 778. The relieving opening 779 canfacilitate adjustment of the characteristics (e.g., flexibility,rebound, and the like) of the locking elements 777 by the selection ofthe shape, position, and/or size of the opening 779.

The drawing of FIG. 11C and the photograph of FIG. 11D depict a stentlocking assembly 771 composing the medial portion 774 disposed to passthrough slot 787 b of the backbone 782. During radial expansion of thestent upon deployment, one or more of the locking elements or teeth 777a can enter the proximal opening of slot 787 b and become deflectedinward by engagement with the slot. This deflection is illustrated bydeflected tooth 777 b, seen together with the superimposed undeflectedshape as a dashed line. It may be seen that, as the adjacent tooth 777 bis deflected, the relieving opening 779 may also deform under thedeflection stress to a deformed shape 779′, shown as a dashed line.

As the tooth element 777 c passes distally beyond slot 787 b, the tooth777 b rebounds to approximately the shape of the un-deflected tooth 777a, so as to prevent radial contraction (proximal motion of rail portion774). Relieving opening 779 may be configured to reduce or eliminateplastic deformation of locking mechanism 776 as the locking elements 777are deflected during slot engagement, so as to improve the rebound ofdeflected tooth 777 b. The shape of tooth 777 a upon rebound isconfigured to inhibit the tooth 777 a from re-entering the distalopening of slot 787 b, so as to inhibit contraction of the stent. Inthis process, the tooth 777 c may deflect outward to increase thepositive nature of the locking assembly 771. The relieving opening 779may deform under the locking stress to form a different shape 779″.

Stent Assemblies with Extended Rail Arrays

FIGS. 12A and 12B depict an alternative stent embodiment 780, in whichadditional modules of rail members are included. Like the embodiment ofFIGS. 9A-9D, the embodiment 780 has at least a first module of railmembers 784 directed in a generally perpendicular direction relative tothe stent axis (e.g., downward in the illustrations of FIGS. 12A and12B), and at least a second module of rail members 785 directedgenerally opposite the first module of rail members 784 and generallyperpendicular relative to the stent axis (e.g., upward in theillustrations of FIGS. 12A and 12B).

In the example shown in FIGS. 12A and 12B, each of the modules 784, 785can comprise a group of three overlapping rail members 784 a-c, 785 a-c.Each rail member can be joined or mounted to at least one backbone(three backbones 782 a-c are illustrated) at attachment point 786. Eachrail member 784 can comprise a plurality of space-apart generallyparallel rails 784′, 784″ that can be connected by a distal cross member784″. Rail members 785 can be similarly structured.

In addition to being proximally mounted to at least one backbone, eachof the individual rails or the rail members 784 a-c, 785 a-c can engageand pass slidably through a slot 787 in an adjacent backbone. Asdiscussed above, although FIGS. 12A and 12B diagrammatically showassembly 780 as planar shape, these figures represent a generallytubular stent assembly 780. As shown by arrow 788 a, the rail members784 c mounted to backbone 782 c can be configured to pass slidablythrough slots of adjacent backbone 782 a, and similarly arrow 788 bindicates that rails member 785 a mounted to backbone 782 a can beconfigured to pass slidably through slots in backbone 782 c.

FIG. 12A illustrates a compacted form of stent assembly 780, in whichthe toothed portion 789 of each rail of rail members 784 a-c, 785 a-c ispositioned distal to the corresponding engagement slot 787 (indicated as787 a). In some embodiments, the backbones 782 a-c are disposed closelyadjacent one another and/or nested. In some embodiments, in thecompacted configuration, the stent 780 is configured to mount on acollapsed balloon catheter.

FIG. 12B illustrates a radially expanded form of the stent assembly 780,in which the toothed portion 789 of each rail of the rail members 784a-c, 785 a-c is positioned at least partially within the correspondingengagement slot 787 (indicated as 787 b). In some embodiments, in theradially expanded state of the stent 780, the backbones 782 a-c aredisposed at a substantial separation from one another, as wouldtypically be configured for deployment at a larger tubular diametersupporting a treated vascular or other body lumen. In this configurationthe toothed portion 789 can inhibit radial contraction of the stent 780.

In the illustrated embodiment, each backbone 782 a-c has an overallslant angle or slope θ (with respect to the stent axis) and can bedisposed as a generally helical portion in the tubular stent body. Insome embodiments, the overall slope angle θ reverses (shown as +θ and −θin FIG. 12A) adjacent each rail module 784, 785, so as to form anoverall zig-zag shape. In the example shown, each backbone includesthree distinct helical portions of substantial pitch, and the stentassembly 780 comprises four rail modules, each oppositely alignedrelative its each adjacent rail modules. In the example shown in FIGS.12A and 12B, the slope angle θ of each portion is about 25 degrees,although it may be greater or less than this.

FIGS. 13A and 13B illustrate end-on views (looking down the open lumen)of the stent 780 in the compacted and expanded stent configurations,respectively. In these figures, stent 780 is viewed as if viewing theperspective view of FIG. 14A looking at the axis of the drawing from theright hand side. The view is, in essence, a cross section of the stentthrough rail member 784 a. These views also correspond to viewing theassembly 780 in FIGS. 12A and 12B from the left hand side of the figureplane (when the stent is in the rolled configuration).

As may be seen in the compacted configuration of FIG. 13A, the railmember 784 a is mounted at its proximal end to backbone 782 a. Railmember 784 a extends clockwise in the figure to pass through slot 787 inadjacent backbone 782 b. As shown, the locking mechanism 776 a normallyis positioned beyond the slot 787 when the stent 780 is in the compactedconfiguration. The other backbone and rail member assemblies 782 b-784b, 782 c-784 c are disposed and configured similarly in clockwisefashion, each rail member 784 b, 784 c also passing through a slot 787in an adjacent backbone. A deflated balloon catheter 800 is representedby phantom lines inside the perimeter defined by the compacted stentassembly 780. In some embodiments, a retractable/removable sheath 802surrounds the compacted stent assembly 780 until the stent is inposition within a lumen at a treatment site.

As may be seen in the radially expanded configuration of FIGS. 13B and14A, the balloon 800 of the catheter assembly has been inflated to anextended diameter 800′, expanding the perimeter of stent assembly 780radially outward. During such expansion, each backbone 782 a-c generallymoves circumferentially farther away from each adjacent backbone than itwas in the compacted state. As a result, each rail member 784 moves withrespect to its respective engagement slot 787 such that after theexpansion the engagement slot 787 is positioned at a more distal portionof the rail member 784. Such movement eventually results in the lockingmechanism 776 being at least partially engaged within the slot with atleast one of the locking elements 777 inhibiting radial contraction ofthe rail member 784, e.g., in the manner shown in FIGS. 11C and 11D.Note that cross member 775 of each rail member lies at the outside theperimeter defined by adjacent rail members, spanning across theseadjacent rail members. Such an arrangement advantageously can maintainthe distal end of the deployed rail member 784 securely outside of thevascular lumen following retraction and removal of the balloon catheter800.

FIG. 14B illustrates a flexed or bent configuration of stent assembly780 as deployed in a curving vascular lumen. In some embodiments, thespring-like configuration and longitudinal continuity of the pluralityof backbones 782 a-c can permit the tubular assembly to be smoothlyflexed to follow a curved lumen. Additionally, in some embodiments, theregular rib-like structure comprising a plurality of circumferentiallyaligned rail members 784 a-c, 785 a-c can provide radial strength andsupport for the lumen wall.

FIGS. 15A and 15B illustrate schematically the relation of the backbones(e.g., 782 a and 782 b) to the rail members 784. FIG. 15A is across-sectional side view of a portion of backbone 782 a, illustratingthe proximal ends 772 a-b of one rail member mounted in backbone recess786 (e.g., by adhesive or solvent bond 786 b), and showing the elongaterail elements 773 a-b on and adjacent rail member passing through theslots 787 a of the backbone. FIG. 15B illustrates a single rail member784 in cross section, having a proximal portion 773 mounted to backbone782 a at recess 786, and passing through slot 787 a of adjacent backbone782 b.

Overall and Localized Backbone Slope

FIG. 16 is a detail of a mid portion of the compacted stent assembly 780shown in FIG. 12A, and the elements are labeled as in FIG. 12A. Asshown, the backbone 782 b can include an overall helix angle for thebackbone portion shown (θ_(oa)). In general, a steeper overall helixangle contributes to a deployed stent that has greater longitudinalflexibility and radial strength. In contrast, a shallower overall helixangle normally contributes to an assembly that may be expanded duringballoon deployment with a reduced tendency to twist as it expands,thereby promoting a smoother and more uniform deployment. The overallhelix angle may be selected to provide desired stent characteristics.For example, in some cases the overall helix angle is selected tobalance between the aforementioned general properties.

In some arrangements, although the overall helix angle θ_(oa) may be inone direction (e.g., positive) a portion of the stent assembly 780 mayinclude one or more regions with an opposite slope (e.g., negative). Forexample, the overall helix angle θ_(oa) may be negative, but a portionof the stent assembly may be positive, before reversing and trendingdownward again. Further, as illustrated in FIG. 17, the backbone cancomprise a plurality of discrete segments. The discrete segments can bethat portion of the backbone extending between engagement elements ofthe backbone. Further, the discrete segments can comprise the portion(s)of the backbone corresponding to the engagement elements of thebackbone. In some embodiments, each of these discrete segments cancomprise a discrete helix angle or slot angle. In some embodiments, suchas when the discrete segment is an engagement element (such as a slot),the discrete helix angle may be referred to as a slot angle. Adiscussion of the overall helix angle and the discrete helix angle orslot angle follows.

Normally, the reversing helical shape of the backbone can comprise atleast one portion that trends positive and at least one portion thattrends negative. A positive trend is a portion or the backbone that hasa positive overall helix angle, regardless of the discrete helix anglesof the individual or discrete segments. A negative trend is a portion orthe backbone that has a negative overall helix angle, regardless of thediscrete helix angles of the individual or discrete segments. In somecases, within one or both of the positive and negative trending portionsthere can be one or more sections that are sloped oppositely to thetrend. For example, a negatively trending portion can include apositively sloped section. Likewise, positively trending portion caninclude a negatively sloped section. Generally, the oppositely slopedsection is minor compared to the trending portion. For example, in someembodiments the oppositely sloped section is less than about 25% of thelength of the trending portion. In some embodiments the oppositelysloped section has an amplitude that is less than about 30% of theamplitude of the trending portion.

Surprisingly, a backbone having a reversing (e.g., a zig-zag) helixangle, such as is shown in FIGS. 12A and 12B, can promote anadvantageous balance between these general properties so as to provideenhanced longitudinal flexibility and radial strength in combinationwith a reduced tendency to twist upon deployment. In contrast, asubstantially continuous overall slope (such as in the backbones of theembodiment of FIGS. 1-3) does not provide the same advantages.

In addition to the generally overall helical alignment of the backboneportions indicated by angle θ_(oa), it may be seen that each helicalportion (e.g., each leg of the zig-zag) has a local reversing helicalshape, e.g., a small-pitch undulation or waviness. Contrast thesmall-pitch undulation or waviness of the backbones 782 a-c of FIGS.12A-12D with the backbone alignment shown in FIG. 9A. This localizednon-uniformity results all or some of the slot 787 having acharacteristic centerline slope incrementally different than the overallslope, the difference denominated dθ₁, dθ₂, dθ₃, dθ₄, . . . dθ_(n).

In the example shown in FIG. 16, each slot portion 787 a hasapproximately the same value of dθ relative to the overall helical angleθ_(oa), although this need not be so. The values of dθ may each bedifferent from adjacent slots and may have a positive variation ornegative variation. For example, FIGS. 17A-C illustrate plan, elevation,and partial focused views of an example backbone 792 that is generallysimilar to the backbone 782 a (shown in FIGS. 12A and 12B) and hasdifferent dθ values. In this example, the overall helix angle of each ofthree slanted portions (the three legs of the zig-zag) is about 25degrees or −25 degrees. As discussed further above, the absolute valueof the overall helix angle of the backbone can be between at least about15 degrees and/or less than or equal to about 60 degrees. The absolutevalue of the overall helix angle of the backbones can also be between atleast about 20 degrees and/or less than or equal to about 50 degrees.Further, the absolute value of the overall helix angle of the backbonescan be between at least about 22 degrees and/or less than or equal toabout 30 degrees. In some embodiments, the absolute value of the overallhelix angle of the backbones can be about 25 degrees. As shown, theplurality of slots 797 are normally distributed longitudinally along thebackbone 792 to provide sliding engagement for an array of rail members,such as members 784, 785 in FIGS. 12A and 12B.

The approximate angle of the mid-line of each slot 797 is indicated. Asshown, this embodiment includes a relatively small slot angle of about10 degrees, and medium slot angle of about 33 degrees and a steeper slotangle of about 40 degrees. Of course, this embodiment is only oneexample and various other slot angle values and arrangements arecontemplated. In some embodiments, the absolute value of the slot anglecan be between at least about 0 degrees and/or less than or equal toabout 60 degrees. The absolute value of the slot angle can also bebetween at least about 10 degrees and/or less than or equal to about 50degrees. Further, the absolute value of the slot angle can be between atleast about 20 degrees and/or less than or equal to about 40 degrees.The slot angle can also vary between at least about 30 degrees and/orless than or equal to about 35 degrees. Finally, as illustrated, theabsolute value of the slot angle can be approximately 10 degrees, 33degrees, 40 degrees. Further, it is contemplated that the slot angle canbe any variety or combination of desired angles that are configured tofacilitate ease of expansion on the one hand and stent flexibility onthe other hand.

For example, in some embodiments, two of the slot angles values areequal. In some embodiments, the middle slot has the greatest slot anglevalue. In some embodiments, at least one of the slot angles values isequal to the overall helical angle θ_(oa). In some embodiments, theaverage or the median of the slot angles values is about equal to theoverall helical angle θ_(oa).

Generally, a steeper slot angle enhances longitudinal flexibility andradial strength of the stent, thereby promoting a stent that is bothstronger and more elastic. In contrast, a shallower slot angle generallyenhances expansion of the stent deployment and reduces the tendency ofthe stent twist as it expands, thereby promoting a stent with a smootherand more uniform deployment.

The individualized slot angles of the slots 797 as provided by thetailored undulations or waiviness of the backbone as shown in FIG. 17Ballows further refinement of deployment characteristics. Surprisingly,it has been found that a slope angle in the region of slot 787 a may beselected to promote more uniform and predictable stent deployment as thestent is radially expanded by a balloon catheter at a selected vasculartreatment site. As discussed above, angles may be selected to promotestrength and flexibility, or a highly uniform deployment behavior. Insome embodiments, angles are selected to promote a sequential openinglongitudinally, for example, configured to match balloon inflationcharacteristics.

As shown in FIGS. 17D and 17E, the slot angle dθ for each slot may bemeasured in at least two locations. As shown in FIG. 17D, in someembodiments, the slot angle dθ is the angle between a line connectingthe midpoints of sidewalls 798 a, 798 b of the slot 797 and a lineparallel with the longitudinal axis of the stent. In other embodiments,the slot angle dθ can be measured as the angle between a tangent to amidpoint of the lower edge 799 of the slot 797 and a line parallel withthe longitudinal axis of the stent, as shown in FIG. 17E.

Additionally, although the above discussion characterizes the backboneas being divided into discrete parts whose angular orientation is takenat the slots of the backbone, the angular orientation of discrete partsof the backbone can also be taken in similar fashion for those segmentsof the backbone extending between the slots of the backbone. Asillustrated in FIG. 17B, the discrete segments extending between theslots of the backbone can be generally curvilinear and define anincreasingly or decreasingly positive slope (as shown on the immediateleft side of a peak along a leg of the backbone) and/or define anincreasingly or decreasingly positive slope (as shown on the immediateright side of a peak along a leg of the backbone).

In some embodiments, these discrete segments can be generallycurvilinear and provide the “rise” or “fall” component of the helicalextension of the backbone while the slot extends generally parallelrelative to the longitudinal axis of the stent. In other words, in someembodiments, only the discrete segments extending between the slotswould extend in a helical direction. However, as discussed extensivelyherein, the incorporation of curved or curvilinear segments in someembodiments can enhance the flexibility and strength of the stent. Inother embodiments, the discrete segments and the slots of the backbonecan all be curvilinear or generally straight and extend in a directiongenerally parallel to the relative to the longitudinal axis or helicallyabout the axis.

Stent Device Manufacture, Processes and Assembly

The overall stent device manufacturing process may include any or all ofthe following sub-steps in any effective operational order:

-   -   Polymer synthesis, compounding and/or mixing.    -   Non-polymer materials, such as a biocompatible metal material,        such as a bioerodable alloy or non-bioerodable alloy. All or        some parts may be metallic, and metal sheet processing steps        below may be functionally equivalent to polymer oriented steps        below.    -   Optional composite materials, e.g., reinforcing materials, drug        carrier particles, and the like.    -   Polymer film pressing, molding and/or thermal processing.    -   Multi-layer film.    -   Drug coating of polymer film.    -   Cutting of parts from polymer film, e.g., laser cutting. In some        embodiments, different parts of the stent may have different        film composition or structure.    -   Industrial precision part forming methods, injection molding,        3-D printing, UV stereo-forming, and the like.    -   Drug coating of formed parts, e.g., anti-restenosis compound        applied in polymer/solvent carrier, such as by spraying,        dipping, or the like.    -   Pre-forming and/or molding of parts, e.g., pre-shaped backbones        and rail members (see, e.g., FIGS. 18, 19A, and 19B).    -   Assembly of stent in semi-compacted configuration, e.g.:        -   tooling to hold and manipulate parts;        -   grooved mandrels to hold backbone assembly,        -   insertion of rail members though slide slots;        -   bonding of rail members in bond recesses or bond-slots (such            as with adhesive bonding, solvent bonding, heat or energy            bonding, or the like);        -   trimming of excess material and/or assembly tabs from parts;            and/or        -   optional post-assembly treating, coating and/or polishing.    -   Inspection and quality control of assembled stent.    -   Final stent compaction and mounting on balloon catheter (e.g.,        iris-like uniform compaction devices, heat, pressure, fluids,        vacuum and/or pressure applied to balloon, and the like).    -   Packaging and sterilization of stent/catheter product (e.g.,        E-beam Irradiation, chemical sterilization, or the like).

The stent can be made from many types of biocompatible materials. Forexample, polymer compositions suitable for making the stent embodimentsdescribed herein are described in published patent applicationUS2010-0228,343, Brandom, et al.; “Phase-Separated Biocompatible PolymerCompositions For Medical Uses”. See, e.g., Tables 2 and 3 of thatpublication, and related description, which teach the preparation andtesting of a copolymers of I₂DTE (di-iodo-desaminotyrosyl tyrosine ethylester) and PCL (polycaprolactone) of different molecular weights, suchas Poly(85% I2DTE-co-8% PCL10K-co-7% PCL1.25K carbonate).

Other biocompatible materials may be employed Likewise, composite and/orlayered materials may be employed. Different parts, such as rail membersand backbones, may have differing polymer composition and/or differentmaterial properties (e.g., different layer structure, heat treatment orannealing history, composite content or the like). In alternativeembodiments combination of polymer and metallic materials may beemployed. Bioerodable metallic materials such as alloys and coatedmetals may be employed for the stent structure without departing fromthe unique and novel aspects disclosed herein. Bioerodable metallicmaterials may comprised magnesium, iron alloys, zinc, manganese and thelike.

FIGS. 18, 19A, and 19B illustrate pre-formed backbone and rail memberparts having a pre-formed shape between the same parts as cut from flatsheet polymer (see, e.g., FIGS. 11, 17A, and 17B) and the shape asfinally assembled in a complete stent structure (such as FIGS. 13A-14B).For example, the parts may be shaped in molds or other tooling byapplication of pressure, heat, optionally moisture, and the like orcombinations of those. Such pre-forming or pre-shaping of parts such asbackbones 782 and rail members 784 may advantageously reduce oreliminate plastic deformation, residual stresses, or other changes tomaterial properties during the process of assembling and mounting thestent. Pre-forming or pre-shaping of parts may also simplify and promoteconvenience in the assembly process, and promote precision in alignmentof parts for bonding or the like.

FIG. 18 shows a typical rail member 784, which has been pre-formed tohave an overall curvature approximating the curved surface of thetubular stent assembly, and in which the proximal rail end portions 772a and 772 b have been given a greater curvature (smaller radius)approximating the curvature of these portions in the compacted stentassembly (see, e.g., FIG. 13A).

FIGS. 19A and 19B show typical backbones 852 and 854 that have beengiven a pre-formed shape approximating the shape in the assembled stent.The backbone 852 in FIG. 19A has a reversing helical shape (see FIGS.14A and 14B), such that only the inside surface 856 (facing towardcenter of assembled stent lumen) is apparent in the plane of thedrawing. In contrast, backbone 854 in FIG. 19B has a continuous helicalshape, in which both inside surface 856 and outside surface 857 (facingoutward from assembled stent lumen) is apparent in the plane of thedrawing.

FIGS. 20A-20D show details of the assembly process of mounting railmembers (e.g., 784-785 of FIGS. 12A and 12B) during assembly, which isapplicable to core bonded assemblies (e.g., embodiments in which therail member is bonded to the backbone) of the various alternativeembodiments described herein. In such assemblies, the typical sequenceis to pass rail members through the sliding slots of the adjacentbackbone prior to fixedly mounting the rail member to its supportingbackbone. In some cases, grooved or conformably-shaped mandrels are usedfor securing the backbones during assembly of the stent structure.

FIGS. 20A and 20B shows the preliminary step of inserting the proximalends of the rail members 772 through the slots 787 in the adjacentbackbone 782 b in the direction shown by the arrow. FIGS. 20C and 20Dshow a subsequent step of fixedly mounting the proximal rail member ends772 to supporting backbone 782 a. In this example, an adhesive bond isformed between the rail end 772 and the surface of recess 786 using abonding agent 860. An amount or portion of bonding agent 860 may bedeposited in recess 786, followed by pressing rail end 772 down intorecess 786. Specialized positioning or clamping tooling may be providedfor convenience and consistency in this mounting process. In oneexample, a bonding agent 860 may comprise a solvent which allows thematerial of backbone 782 to adhere to the material of rail end 772. Forexample, an agent comprising methylene chloride or a similar solvent maybe applied to bond polymer parts comprising a copolymer of I₂DTE andPCL. In other examples, agent 860 may comprise cross-linking or UVcurable adhesive. In yet another example, energy such a locally appliedheat or ultrasound may be used to bond rail 772 to backbone 782. In yetother examples, a fitting or fastener may be employed.

Testing Data of Stent Embodiments Compared to Prior Art Stents

As discussed herein, embodiments of the helical slide-and-lock stentscan provide superior flexibility and stiffness compared to prior polymerstents. In this regard, various tests have shown that the stiffness ofembodiments disclosed herein is greater than that of prior art polymerstents. Indeed, the structural properties, such as the stiffness, ofembodiments disclosed herein more closely mimics the structuralproperties of metal stents.

Accordingly, embodiments of the stents disclosed herein represent asignificant advance in stent technology which allows a polymer and/orcomposite material to be used in a configuration that providesstructural properties that can approach and/or replicate the structuralproperties of a metal stent. Metal stents have the disadvantage of notbeing as bioresorbable as polymer stents; however, metal stents havelong provided superior structural properties that may be needed forsevere lesions, such as rigidity, stiffness, and crush strength. Incontrast, prior polymer stents could provide resorbability and otherbenefits not available with metal stents; however, prior polymer stentwere not as stiff, rigid, or strong as the metal counterparts. One ofthe solutions and advances made by embodiments of the stent of thepresent application is the provision of a manner of achievingbioresorbability and the other benefits of polymers while exhibitingsuperior structural properties similar to metal stents. Indeed, theunique features and configurations of the helical slide-and-lock polymerstents disclosed herein enable one of skill to obtain the benefits ofpolymer and metal stents. Further, the present disclosure also providesfor a variety of stents having a composite material structure which canincorporate advantages of various materials.

Lamination Manufacturing Process Embodiments

Stents in accordance with embodiments can be fabricated or created usinga wide variety of manufacturing methods, techniques and procedures.These include, but are not limited to, laser processing, milling,stamping, forming, casting, molding, bonding, welding, adhesivelyfixing, and the like, among others.

In some embodiments, stent features and mechanisms can be created in agenerally two dimensional geometry and further processed, for example byutilizing, but not limited to, bonding, lamination and the like, intothree dimensional designs and features. In other embodiments, stentfeatures and mechanisms can be directly created into three dimensionalshapes, for example by utilizing, but not limited to, processes such asinjection molding and the like.

In certain embodiments, stents can be fabricated by using an injectionmolding process, technique or method. For example, an injection moldingprocess or the like, among others, can be used to form stent rows asintegral units. The axially extending rows can then be connected androlled into a tubular form in the collapsed state.

In some embodiments, a lamination stack can used to fabricate the stentrows by a lamination process in accordance with one embodiment. Theaxially extending rows can then be connected and rolled into a tubularform in the collapsed state.

The lamination stack, in some embodiments, generally can comprise threesheets or pallets which can have the desired features formed thereon,for example, by laser cutting, etching and the like. The pallets can bealigned and joined, for example, by bonding, welding and the like toform a unit. The excess material (e.g., side and end rails) can beremoved to form the stent rows. The pallets can include variouscircumferentially nesting features such as male and female articulatingand/or ratcheting designs to control and limit the diameter in collapsedand fully deployed states.

Stent Materials Generally

The stent can be fabricated from at least one or more materials. Thesematerials include metals, polymers, composites, and shape-memorymaterials. In another optional embodiment, the stent further cancomprise a tubular member formed from a biocompatible and preferably,bioresorbable polymer, such as those disclosed in co-pending U.S.application Ser. No. 10/952,202, the disclosure of which is incorporatedherein in its entirety by reference. It is also understood that thevarious polymer formulae employed can include homopolymers andheteropolymers, which can include stereoisomerism, composites, filledmaterials, etc. Homopolymer is used herein to designate a polymercomprised of all the same type of monomers. Heteropolymer is used hereinto designate a polymer comprised of two or more different types ofmonomer which is also called a co-polymer. A heteropolymer or copolymercan be of a kind known as block, random and alternating. Further withrespect to the presentation of the various polymer formulae, productsaccording to embodiments can be comprised of a homopolymer,heteropolymer and/or a blend of such polymers.

The term “bioresorbable” is used herein to designate polymers thatundergo biodegradation (through the action of water and/or enzymes to bechemically degraded) and at least some of the degradation products canbe eliminated and/or absorbed by the body. The term “radiopaque” is usedherein to designate an object or material comprising the object visibleby in vivo analysis techniques for imaging such as, but not limited to,methods such as x-ray radiography, fluoroscopy, other forms ofradiation, MRI, electromagnetic energy, structural imaging (such ascomputed or computerized tomography), and functional imaging (such asultrasonography). The term “inherently radiopaque” is used herein todesignate polymer that is intrinsically radiopaque due to the covalentbonding of halogen species to the polymer. Accordingly, the term doesencompass a polymer which is simply blended with a halogenated speciesor other radiopacifying agents such as metals and their complexes.

In another optional variation, the stent further can comprise an amountof a therapeutic agent (for example, a pharmaceutical agent and/or abiologic agent) sufficient to exert a selected therapeutic effect. Theterm “pharmaceutical agent”, as used herein, encompasses a substanceintended for mitigation, treatment, or prevention of disease thatstimulates a specific physiologic (metabolic) response. The term“biological agent”, as used herein, encompasses any substance thatpossesses structural and/or functional activity in a biological system,including without limitation, organ, tissue or cell based derivatives,cells, viruses, vectors, nucleic acids (animal, plant, microbial, andviral) that can be natural and recombinant and synthetic in origin andof any sequence and size, antibodies, polynucleotides, oligonucleotides,cDNA's, oncogenes, proteins, peptides, amino acids, lipoproteins,glycoproteins, lipids, carbohydrates, polysaccharides, lipids,liposomes, or other cellular components or organelles for instancereceptors and ligands. Further the term “biological agent”, as usedherein, can include virus, serum, toxin, antitoxin, vaccine, blood,blood component or derivative, allergenic product, or analogous product,or arsphenamine or its derivatives (or any trivalent organic arseniccompound) applicable to the prevention, treatment, or cure of diseasesor injuries of man (per Section 351(a) of the Public Health Service Act(42 USC 262(a)). Further the term “biological agent” can include 1)“biomolecule”, as used herein, encompassing a biologically activepeptide, protein, carbohydrate, vitamin, lipid, or nucleic acid producedby and purified from naturally occurring or recombinant organisms,tissues or cell lines or synthetic analogs of such molecules, includingantibodies, growth factors, interleukins and interferons; 2) “geneticmaterial” as used herein, encompassing nucleic acid (eitherdeoxyribonucleic acid (DNA) or ribonucleic acid (RNA), genetic element,gene, factor, allele, operon, structural gene, regulator gene, operatorgene, gene complement, genome, genetic code, codon, anticodon, messengerRNA (mRNA), transfer RNA (tRNA), ribosomal extrachromosomal geneticelement, plasmagene, plasmid, transposon, gene mutation, gene sequence,exon, intron, and, 3) “processed biologics”, as used herein, such ascells, tissues or organs that have undergone manipulation. Thetherapeutic agent can also include vitamin or mineral substances orother natural elements.

In some embodiments, the design features of the axially orcircumferentially offset elements can be varied to customize thefunctional features of strength, compliance, radius of curvature atdeployment and expansion ratio. In some embodiments, the stent cancomprise a resorbable material and vanishes when its job is done. Insome embodiments, the stent serves as a therapeutic delivery platform.

Some aspects are also disclosed in co-pending U.S. patent applicationSer. Nos. 11/016,269, 60/601,526, 10/655,338, 10/773,756, and10/897,235, the disclosures of each of which are incorporated herein intheir entirety by reference thereto.

Some features and arrangements of embodiments of stents are disclosed inU.S. Pat. Nos. 6,033,436, 6,224,626, and 6,623,521, each issued toSteinke, the disclosures of each of which are hereby incorporated intheir entirety by reference thereto.

Advantageously, the stent design elements and interlocks can be variedto customize the functional features of strength, compliance, radius ofcurvature at deployment and expansion ratio. In some embodiments, thestent can comprise a resorbable material and vanishes when its job isdone. In some embodiments, the stent serves as a delivery platform fortherapeutic agents such as pharmaceutical compounds or biologicalmaterials.

Metal Stents and Methods of Manufacturing

Possible materials for making the stents in accordance with someembodiments include cobalt chrome, 316 stainless steel, tantalum,titanium, tungsten, gold, platinum, iridium, rhodium and alloys thereofor pyrolytic carbon. In still other alternative embodiments, the stentscan be formed of a corrodible material, for instance, a magnesium alloy.Although various stent embodiments have been described as beingconventional balloon expandable stents, those skilled in the art willappreciate that stent constructions according to embodiments can also beformed from a variety of other materials to make a stentcrush-recoverable. For example, in alternative embodiments, such as selfexpandable stents, shape memory alloys that allow for such, such asNitinol and Elastinite®, can be used in accordance with embodiments.

Various methods of forming the individual elements from metal sheets cancomprise laser cutting, laser ablation, die-cutting, chemical etching,plasma etching and stamping and water jet cutting of either tube or flatsheet material or other methods known in the art which are capable ofproducing high-resolution components. The method of manufacture, in someembodiments, depends on the material used to form the stent. Chemicaletching provides high-resolution components at relatively low price,particularly in comparison to high cost of competitive product lasercutting. Some methods allow for different front and back etch artwork,which could result in chamfered edges, which can be desirable to helpimprove engagements of lockouts. Further one can use plasma etching orother methods known in the art which are capable of producinghigh-resolution and polished components. The embodiments disclosedherein are not limited to the means by which stent or stent elements canbe fabricated.

Once the base geometry is achieved, the elements can be assemblednumerous ways. Tack-welding, adhesives, mechanical attachment(snap-together and/or weave together), and other art-recognized methodsof attachment, can be used to fasten the individual elements. Somemethods allow for different front and back etch artwork, which couldresult in chamfered edges, which can be desirable to help improveengagements of lockouts. In an advantageous method of manufacture, thecomponents of the stent can be heat set at various desired curvatures.For example, the stent can be set to have a diameter equal to that ofthe deflated balloon, as deployed, at a maximum diameter, or greaterthan the maximum diameter. In yet another example, elements can beelectropolished and then assembled, or electropolished, coated, and thenassembled, or assembled and then electropolished.

Polymeric Stents

While metal stents possess certain desirable characteristics, the usefullifespan of a stent is estimated to be in the range of about 6 to 9months, the time at which in-stent restenosis stabilizes and healingplateaus. In contrast to a metal stent, a bioresorbable stent cannotoutlive its usefulness within the vessel. Moreover, a bioresorbablestent could potentially be used to deliver a greater dose of atherapeutic agent, deliver multiple therapeutic agents at the same timeor at various times of its life cycle, to treat specific aspects orevents of vascular disease. Additionally, a bioresorbable stent can alsoallow for repeat treatment of the same approximate region of the bloodvessel. Accordingly, there remains an important unmet need to developtemporary (i.e., bioresorbable and/or radiopaque) stents, wherein thepolymeric materials used to fabricate these stents can have thedesirable qualities of metal (e.g., sufficient radial strength andradiopacity, etc.), while circumventing or alleviating the manydisadvantages or limitations associated with the use of permanent metalstents.

In some embodiments, the stent can be formed from biocompatible polymersthat are bio-resorbable (e.g., bio-erodible or bio-degradable).Bio-resorbable materials can be preferably selected from the groupconsisting of any hydrolytically degradable and/or enzymaticallydegradable biomaterial. Examples of suitable degradable polymersinclude, but are not limited to, polyhydroxybutyrate/polyhydroxyvaleratecopolymers (PHV/PHB), polyesteramides, polylactic acid, polyglycolicacid, lactone based polymers, polycaprolactone, poly(propylenefumarate-co-ethylene glycol) copolymer (aka fumarate anhydrides),polyamides, polyanhydride esters, polyanhydrides, polylacticacid/polyglycolic acid with a calcium phosphate glass, polyorthesters,silk-elastin polymers, polyphosphazenes, copolymers of polylactic acidand polyglycolic acid and polycaprolactone, aliphatic polyurethanes,polyhydroxy acids, polyether esters, polyesters, polydepsidpetides,polysaccharides, polyhydroxyalkanoates, and copolymers thereof. Foradditional information, see U.S. Pat. Nos. 4,980,449, 5,140,094, and5,264,537, the disclosures of each of which are incorporated byreference herein.

In one mode, the degradable materials can be selected from the groupconsisting of poly(glycolide-trimethylene carbonate), poly(alkyleneoxalates), polyaspartimic acid, polyglutarunic acid polymer,poly-p-dioxanone, poly-.beta.-dioxanone, asymmetrically 3,6-substitutedpoly-1,4-dioxane-2,5-diones, polyalkyl-2-cyanoacrylates,polydepsipeptides (glycine-DL-lactide copolymer), polydihydropyranes,polyalkyl-2-cyanoacrylates, poly-.beta.-maleic acid (PMLA),polyalkanotes and poly-.beta.-alkanoic acids. There are many otherdegradable materials known in the art. (See e.g., Biomaterials Science:An Introduction to Materials in Medicine (29 Jul., 2004) Ratner,Hoffman, Schoen, and Lemons; and Atala, A., Mooney, D. SyntheticBiodegradable Polymer Scaffolds. 1997 Birkhauser, Boston; each of whichare incorporated herein by reference).

Further still, in another embodiment, the stents can be formed of apolycarbonate material, such as, for example, tyrosine-derivedpolycarbonates, tyrosine-derived polyarylates, tyrosine-derived diphenolmonomers, iodinated and/or brominated tyrosine-derived polycarbonates,iodinated and/or brominated tyrosine-derived polyarylates. Foradditional information, see U.S. Pat. Nos. 5,099,060, 5,198,507,5,587,507, which was resiussed in U.S. Pat. Nos. RE37,160, 5,670,602,which was resiussed in U.S. Pat. Nos. RE37,795, 5,658,995, 6,048,521,6,120,491, 6,319,492, 6,475,477, 5,317,077, and 5,216,115, and U.S.application Ser. No. 09/350,423, the disclosures of each of which areincorporated by reference herein. In yet another embodiment, the polymercan be any of the biocompatible, bioabsorbable, radiopaque polymersdisclosed in: U.S. Patent Application Nos. 60/852,513, 60/852,471,60/601,526, 60/586,796, 60/866,281, 60/885,600, 10/952,202, 11/176,638,11/335,771, 11/200,656, 11/024,355, 10/691,749, 11/418,943, and11/873,362; U.S. Patent Publication No. US26115449A1; U.S. Pat. Nos.6,852,308 and 7,056,493; and PCT Application Nos. PCT/US2005/024289,PCT/US2005/028228, PCT/US07/01011, and PCT/US07/81571, the disclosuresof each of which are incorporated herein by reference thereto.

Natural polymers (biopolymers) include any protein or peptide.Biopolymers can be selected from the group consisting of alginate,cellulose and ester, chitosan, collagen, dextran, elastin, fibrin,gelatin, hyaluronic acid, hydroxyapatite, spider silk, cotton, otherpolypeptides and proteins, and any combinations thereof.

In yet another alternative embodiment, shape-shifting polymers can beused to fabricate stents constructed according to embodiments. Suitableshape-shifting polymers can be selected from the group consisting ofpolyhydroxy acids, polyorthoesters, polyether esters, polyesters,polyamides, polyesteramides, polydepsidpetides, aliphatic polyurethanes,polysaccharides, polyhydroxyalkanoates, and copolymers thereof. Foraddition disclosure on bio-degradable shape-shifting polymers, see U.S.Pat. Nos. 6,160,084 and 6,284,862, the disclosures of each of which areincorporated by reference herein. For additional disclosure on shapememory polymers, see U.S. Pat. Nos. 6,388,043 and 6,720,402, thedisclosures of each of which are incorporated by reference herein.Further the transition temperature can be set such that the stent can bein a collapsed condition at a normal body temperature. However, with theapplication of heat during stent placement and delivery, such as via ahot balloon catheter or a hot liquid (e.g., saline) perfusion system,the stent can expand to assume its final diameter in the body lumen.When a thermal memory material is used, it can provide acrush-recoverable structure.

Further still, stents can be formed from biocompatible polymers that arebiostable (e.g., non-degrading and non-erodible). Examples of suitablenon-degrading materials include, but are not limited to, polyurethane,Delrin, high density polyethylene, polypropylene, and poly(dimethylsiloxane).

In some embodiments, the layers can comprise or contain any example ofthermoplastics, such as the following, among others: fluorinatedethylene-propylene, poly(2-hydroxyethyl methacrylate) (aka pHEMA),poly(ethylene terephthalate) fiber (aka Dacron®) or film (Mylar®),poly(methyl methacrylate) (aka PMMA), Poly(tetrafluoroethylene) (akaPTFE and ePTFE and Gore-Tex®), poly(vinyl chloride), polyacrylates andpolyacrylonitrile (PAN), polyamides (aka Nylon), polycarbonates andpolycarbonate urethanes, polyethylene and poly(ethylene-co-vinylacetate), polypropylene, polystyrene, polysulphone, polyurethane andpolyetherurethane elastomers such as Pellethane® and Estane®, Siliconerubbers, Siloxane, polydimethylsiloxane (aka PDMS), Silastic®,Siliconized Polyurethane.

Finally, the polymer(s) utilized in embodiments of the stent can befabricated according to any variety of processes, such as thosediscussed in U.S. Patent Application Nos. 60/852,471 and 60/852,513, andU.S. Pat. Nos. 5,194,570, 5,242,997, 6,359,102, 6,620,356, and6,916,868, the disclosures of each of which are incorporated byreference herein.

Methods of Manufacturing and Assembling Polymeric Stents

Where plastic and/or degradable materials are used, the elements can bemade using laser ablation with a screen, stencil or mask; solventcasting; forming by stamping, embossing, compression molding,centripetal spin casting and molding; extrusion and cutting,three-dimensional rapid prototyping using solid free-form fabricationtechnology, stereolithography, selective laser sintering, or the like;etching techniques comprising plasma etching; textile manufacturingmethods comprising felting, knitting, or weaving; molding techniquescomprising fused deposition modeling, injection molding, roomtemperature vulcanized molding, or silicone rubber molding; castingtechniques comprising casting with solvents, direct shell productioncasting, investment casting, pressure die casting, resin injection,resin processing electroforming, or injection molding or reactioninjection molding. Certain embodiments with the disclosed polymers canbe shaped into stents via combinations of two or more thereof, and thelike.

Such processes can further include two-dimensional methods offabrication such as cutting extruded sheets of polymer, via lasercutting, etching, mechanical cutting, or other methods, and assemblingthe resulting cut portions into stents, or similar methods ofthree-dimensional fabrication of devices from solid forms. Foradditional information, see U.S. patent application Ser. No. 10/655,338,the disclosure of which is incorporated by reference herein.

Stents of some of the embodiments can be manufactured with elementsprepared in full stent lengths or in partial lengths of which two ormore are then connected or attached. If using partial lengths, two ormore can be connected or attached to comprise a full length stent. Inthis arrangement the parts can be assembled to give rise to a centralopening. The assembled full or partial length parts and/or modules canbe assembled by inter-weaving them in various states, from a collapsedstate, to a partially expanded state, to an expanded state.

Further, elements can be connected or attached by solvent or thermalbonding, or by mechanical attachment. If bonding, advantageous methodsof bonding comprise the use of ultrasonic, radiofrequency or otherthermal methods, and by solvents or adhesives or ultraviolet curingprocesses or photoreactive processes. The elements can be rolled bythermal forming, cold forming, solvent weakening forming andevaporation, or by preforming parts before linking.

Rolling of the flat series of module(s) to form a tubular member can beaccomplished by any means known in the art, including rolling betweentwo plates, which can be each padded on the side in contact with thestent elements. One plate can be held immobile and the other can movelaterally with respect to the other. Thus, the stent elements sandwichedbetween the plates can be rolled about a mandrel by the movement of theplates relative to one another. Alternatively, 3-way spindle methodsknown in the art can also be used to roll the tubular member. Otherrolling methods that can be used in accordance with certain embodimentsinclude those used for “jelly-roll” designs, as disclosed for example,in U.S. Pat. Nos. 5,421,955, 5,441,515, 5,618,299, 5,443,500, 5,649,977,5,643,314 and 5,735,872, the disclosures of each of which areincorporated herein in their entireties by reference thereto.

The construction of the slide-and-lock stents in these fashions canprovide a great deal of benefit over the prior art. The construction ofthe locking mechanism can be largely material-independent. This allowsthe structure of the stent to comprise high strength materials, notpossible with designs that require deformation of the material tocomplete the locking mechanism. The incorporation of these materialswill allow the thickness required of the material to decrease, whileretaining the strength characteristics of thicker stents. In someembodiments, the frequency of catches, stops or teeth present onselected circumferential elements can prevent unnecessary recoil of thestent subsequent to expansion.

Radiopacity

Traditional methods for adding radiopacity to a medical product includethe use of metal bands, inserts and/or markers, electrochemicaldeposition (i.e., electroplating), or coatings. The addition ofradiopacifiers (i.e., radiopaque materials) to facilitate tracking andpositioning of the stent could be accommodated by adding such an elementin any fabrication method, by absorbing into or spraying onto thesurface of part or all of the device. The degree of radiopacity contrastcan be altered by element content.

For plastics and coatings, radiopacity can be imparted by use ofmonomers or polymers comprising iodine or other radiopaque elements,i.e., inherently radiopaque materials. Common radiopaque materialsinclude barium sulfate, bismuth subcarbonate, and zirconium dioxide.Other radiopaque elements include: cadmium, tungsten, gold, tantalum,bismuth, platinum, iridium, and rhodium. In some embodiments, a halogensuch as iodine and/or bromine can be employed for its radiopacity andantimicrobial properties.

Multi-Material Vascular Prosthesis

In still other alternative embodiments, various materials (e.g., metals,polymers, ceramics, and therapeutic agents) can be used to fabricatestent embodiments. The embodiments can comprise: 1) differentiallylayered materials (through stacking in the vertical or radial axis) tocreate a stack of materials (materials can be stacked in anyconfiguration, e.g., parallel, staggered, etc.); 2) spatially localizedmaterials which can vary along the long axis and/or thickness of thestent body; 3) materials that are mixed or fused to create a compositestent body (e.g., whereby a therapeutic agent(s) is within the stentbody with a polymer); 4) embodiments whereby a material can be laminated(or coated) on the surface of the stent body (see Stent Surface Coatingswith Functional Properties as well as see Therapeutic Agents Deliveredby Stents); and, 5) stents comprised of 2 or more parts where at leastone part can be materially distinct from a second part, or anycombination thereof.

The fashioning of a slide-and-lock multi-material stent can have betweentwo or more materials. Thickness of each material can vary relative toother materials. This approach as needed or desired allows an overallstructural member to be built with each material having one or morefunctions contributing towards enabling prosthesis function which caninclude, but is not limited to: 1) enabling mechanical properties forstent performance as defined by ultimate tensile strength, yieldstrength, Young's modulus, elongation at yield, elongation at break, andPoisson's ratio; 2) enabling the thickness of the substrate, geometricalshape (e.g., bifurcated, variable surface coverage); 3) enablingchemical properties of the material that bear relevance to the materialsperformance and physical state such as rate of degradation andresorption (which can impact therapeutic delivery), glass transitiontemperature, melting temperature, molecular weight; 4) enablingradiopacity or other forms of visibility and detection; 5) enablingradiation emission; 6) enabling delivery of a therapeutic agent (seeTherapeutic Agents Delivered by Stents); and 7) enabling stent retentionand/or other functional properties (see Stent Surface Coatings withFunctional Properties).

In some embodiments, the materials can comprise load-bearing properties,elastomeric properties, mechanical strength that can be specific to adirection or orientation e.g., parallel to another material and/or tothe long axis of the stent, or perpendicular or uniform strength toanother material and/or stent. The materials can comprise stiffeners,such as the following, boron or carbon fibers, pyrolytic carbon.Further, stents can be comprised of at least one re-enforcement such afibers, nanoparticles or the like.

In another implementation of some embodiments, the stent can be made, atleast in part, from a polymeric material, which can be degradable. Themotivation for using a degradable stent can be that the mechanicalsupport of a stent can only be necessary for several weeks. In someembodiments, bioresorbable materials with varying rates of resorptioncan be employed. For additional information, see U.S. patent applicationSer. Nos. 10/952,202 and 60/601,526, the disclosures of each of whichare incorporated by reference herein. Degradable polymeric stentmaterials can be particularly useful if it also controls restenosis andthrombosis by delivering pharmacologic agents. Degradable materials canbe well suited for therapeutic delivery (see Therapeutic AgentsDelivered by Stents).

In some embodiments, the materials can comprise or contain any class ofdegradable polymer as previously defined. Along with variation in thetime of degradation and/or resorption the degradable polymer can haveother qualities that are desirable. For example, in some embodiments thematerials can comprise or contain any example of natural polymers(biopolymers) and/or those that degrade by hydrolytic and/or enzymaticaction. In some embodiments, the material can comprise or contain anyexample of hydrogels that can or cannot be thermally reversiblehydrogels, or any example of a light or energy curable material, ormagnetically stimulateable (responding) material. Each of theseresponses can provide for a specific functionality.

In some embodiments, the materials can comprise or be made from or withconstituents which can have some radiopaque material alternatively, aclinically visible material which can be visible by x-ray, fluoroscopy,ultrasound, MRI, or Imatron Electron Beam Tomography (EBT).

In some embodiments, one or more of the materials can emit predeterminedor prescribed levels of therapeutic radiation. In an embodiment, thematerial can be charged with beta radiation. In another embodiment, thematerial can be charged with Gamma radiation. In yet another embodiment,the material can be charged with a combination of both Beta and Gammaradiation. Stent radioisotopes that can be used include, but are notlimited to, 103Pd and 32P (phosphorus-32) and two neutron-activatedexamples, 65Cu and 87Rb2O, (90)Sr, tungsten-188 (188).

In some embodiments, one or more of the materials can comprise orcontain a therapeutic agent. The therapeutic agents can have unique,delivery kinetics, mode of action, dose, half-life, purpose, et cetera.In some embodiments, one or more of the materials comprise an agentwhich provides a mode and site of action for therapy for example by amode of action in the extracellular space, cell membrane, cytoplasm,nucleus and/or other intracellular organelle. Additionally an agent thatserves as a chemoattractant for specific cell types to influence tissueformation and cellular responses for example host-biomaterialinteractions, including anti-cancer effects. In some embodiments, one ormore of the materials deliver cells in any form or state of developmentor origin. These could for example be encapsulated in a degradablemicrosphere, or mixed directly with polymer, or hydrogel and serve asvehicle for pharmaceutical delivery. Living cells could be used tocontinuously deliver pharmaceutical type molecules, for instance,cytokines and growth factors. Nonliving cells can serve as a limitedrelease system. For additional concepts of therapeutic delivery, see thesection entitled: Therapeutic Agents Delivered by Stents.

Therapeutic Agents Delivered by Stents

In another implementation, the stent further can comprise an amount of atherapeutic agent (as previously defined for a pharmaceutical agentand/or a biologic agent) sufficient to exert a selected therapeuticeffect. The material of at least a portion of the stent itself cancomprise at least one therapeutic agent, or at least one therapeuticagent can be added to the stent in a subsequent forming process or step.In some embodiments of the stent (e.g., polymer stents andmulti-material stents), the therapeutic agent can be contained withinthe stent as the agent is blended with the polymer or admixed by othermeans known to those skilled in the art.

For example, one or more therapeutic agents can be delivered through amulti-material vascular prosthesis. In some embodiments, the entirestent can be formed from materials comprising one or more therapeuticagents. In other embodiments, portions of the stent, such as individualcomponents thereof, can comprise materials comprising one or moretherapeutic agents. In such embodiments, it is contemplated that thetherapeutic agent(s) can be released as the stent material degrades.

For example, the therapeutic agent can be embedded or impregnated intothe film by means of a combination of solvent casting and thermalpressing. In such a method, the film can be formed from a mixture of thepolymer and the therapeutic agent (20% solids polymer, for examplepoly(90% DTE-co-10% DT carbonate), which can be made with 1% rapamycinin dichloromethane). Once this mixture is prepared, the film can be castusing a doctor blade. Alternatively, the film can be formed by using amechanical reverse roll coater or other solvent-based film caster. Oncethe film is cast, the solvent can be evaporated off using a vacuum oven,e.g., for a period of time and at a temperature suitable for the polymerand drug, such as at 40° C. for at least 20 hours. Once the film isdried, it can be thermally pressed, e.g., at a temperature of 100° C.between two heated platens of a hydraulic press. This allows the potencyof the drug to be retained.

In addition, the therapeutic agent can be embedded or impregnated intothe film using only a solvent or by spin casting. Once a therapeuticagent is selected, one needs to determine if the solvent is compatiblewith the agent and the polymer chosen. The objective is to prepare asuitable sprayable suspension. Additionally, the stability of the drugcan be measured such that the therapeutic agent can remain active whilein the coating as well under physiological conditions once released fromthe film. This can be determined by those skilled in the art who conductstandard in vitro elution studies (see Dhanikula et al., Development andCharacterization of Biodegradable Chitosan Films for Local Delivery ofPaclitaxel, The AAPS Journal, 6 (3) Article 27 (2004),http://www.aapsj.org/view.asp?art=aapsj060327; and Kothwala et al.,Paclitaxel Drug Delivery from Cardiovascular Stent, Trends inBiomaterials & Artificial Organs, Vol. 19(2), 88-92 (2006),http://medind.nic.in/taa/t06/i1/taat06i1p88.pdf) of agent embedded filmsand through the use of analytical methods such as HPLC methods (seeDhanikula et al., Development and Characterization of BiodegradableChitosan Films for Local Delivery of Paclitaxel; and Kothwala et al.,Paclitaxel Drug Delivery from Cardiovascular Stent) to detect the purityof the drug.

In other embodiments, at least one therapeutic agent can be added to thestent and/or its components after the formation of the stent and/or itscomponents. For example, at least one therapeutic agent can be added toindividual stent components, through a coating process or otherwise. Theaddition of at least one therapeutic agent can occur before or aftercutting or lasing of the stent components. In another example, at leastone therapeutic agent can also be added to at least a portion of thestent after partial or full assembly thereof, through a coating processor otherwise. In some embodiments of the stent, the therapeutic agentcan be delivered from a polymer coating on the stent surface. In otherembodiments of the stent, a therapeutic agent can be localized in oraround a specific structural aspect of the device.

For example, the therapeutic agent can be delivered from a polymercoating on the stent surface. Thus, the stent can be made by applyingthe therapeutic agent to a stent component before the stent is assembledor formed. In this regard, the stent component can be created from apolymer sheet, such as a flat polymer film. Thus, at least one stentcomponent can be separated from a remainder or excess portion of thefilm either before or after the therapeutic agent has been applied tothe stent component and/or film. After the therapeutic agent is appliedand the stent component is separated from the film, the stent componentcan be assembled (and in some embodiments, with other stent components)to form a stent therefrom.

In some embodiments, the stent can be prepared with the followingpreparation method. The stent can be initially prepared by creating apattern of a stent component on a flat polymer film. The creation of thepattern on the film can occur before or after application of atherapeutic agent thereto, as discussed below. The pattern of the stentcomponent can be created on the film such that the stent component canbe detached from the film when desired. In some embodiments, the patterncan be created using a laser to lase the pattern onto the film.Additionally, the lased pattern can be of any given stent componentdesign, such as that used in a slide and lock stent design. After thepattern is created on the film, the entire film can be cleaned. Forexample, if the therapeutic agent has not yet been applied to the film,the entire lased film can be immersed into a cleaning solution that iscompatible with the specific type of polymer from which the film ismade. The cleaned film can then be dried, for example, by being blownand oven dried.

A coating formulation can be prepared by dissolving or dispersing thepolymer and the therapeutic agent(s) of choice and solvent(s) or othercompatible excipient(s) using a calculated amount of each component toachieve the desired concentration. The coating formulation can then beapplied to the lased polymer film using one or more coating methods. Forexample, the film may be coated by means of spraying, dipping, or othercoating methods. Additionally cross-linking reagents may also be used toprepare a coating.

In a spraying coating method, the lased polymer films can be coated withthe coating formulation by first mounting the cleaned dried films into aspray apparatus. The coating formulation can then be sprayed onto thefilm, and the film can be rotated 180 degrees such that the other sidecan be coated if desired. This method can allow for coating of one orboth sides of the stent component(s). This method can also allow one toapply different therapeutic agents per side of the lased film and/orstent component and to selectively coat regions thereof. The method canfurther allow one to coat multiple drugs per film and/or stentcomponent. Alternative coating methods can allow for other similarbenefits.

For example, a therapeutic agent can be coated onto a film or stentcomponent as in the following illustration. First, the therapeutic agentin this example is a Polymer-Paclitaxel Formulation, such as a 0.5% [25%Paclitaxel/75% Poly(86.75% I2DTE-co-10% I2DT-co-3.25% PEG2000carbonate)] in tetrahydrofuran (THF), which can be prepared using ananalytical balance. In order to do so, one must first weigh 0.0150 g ofPaclitaxel into a tared vial. Then weigh 0.0450 g of polymer intoanother vial. Next, weigh 11.940 g of THF into each vial. Shake thevials on a laboratory shaker, such as a Roto-genie, for at least onehour. In this example, coating can be achieved using a spray gunapparatus, such as an air brush (see Westedt, U., BiodegradablePaclitaxel-loaded Nanoparticles and Stent Coatings as Local DeliverySystems for the Prevention of Restenosis—Dissertation, Marburg/Lahn(2004),http://deposit.ddb.de/cgi-bin/dokserv?idn=972868100&dokvar=dl&dokext=pdf&filename=972868100.pdf;and Berger, H. L. Using Ultrasonic Spray Nozzles to Coat Drug-ElutingStents, Medical Device Technology (2006),http://www.devicelink.com/mdt/archive/06/11/004.html). Typically, thespray gun apparatus should first be cleaned with THF. In order to do so,a syringe can be filled with at least 10 ml of THF. The syringe can thenbe attached to a spray line attached to the spray gun. Gradually, the 10ml of THF can be pushed from the syringe into the spray gun without N2pressure. This can be repeated as necessary to ensure that the line iswashed clean. The syringe pump can then be set up with the syringecontaining the Polymer-Paclitaxel Formulation.

Next, a film, which can be either lased or unlased, can be placed into ahooded environment and mounted or clipped into a holder. If necessary,the surfaces of the film can be cleaned of lint and dust using a pureair or gas source or equivalent. For consistent coating quality, thefilm can be programmed to move at a set rate (distance and speed)relative to a spray stream by integrating the film holder apparatus witha motion control system. Manual coating without the motion control canalso be used to achieve a coating. The spray gun can also be set todirect the spray to only a given location to control coatingdistribution.

In some embodiments, to coat both sides of the film uniformly, the spraycycle can start with the spray hitting at the bottom corner of the film,and the motion control should move the film incrementally as ittraverses back and forth in front of the spray nozzle. The system canthen move the film back to the start position so the spray is directedat the bottom. The film holder can be turned 180 degrees and the cyclecan be repeated to coat the second side. After coating, the film holdercan be removed with the film and the film can be dried in a vacuum ovenat a temperature suitable for the drug and polymer, e.g., 25°±5° C. forat least 20 hours.

Other methods and teachings related to impregnation or coating processesare found in the following references, the entirety of each of which ishereby incorporated by reference herein: Westedt, U., BiodegradablePaclitaxel-loaded Nanoparticles and Stent Coatings as Local DeliverySystems for the Prevention of Restenosis—Dissertation, Marburg/Lahn(2004),http://depositddb.de/cgi-bin/dokserv?idn=972868100&dokvar=dl&dokext=pdf&filename=972868100.pdf;Berger, H. L. Using Ultrasonic Spray Nozzles to Coat Drug-ElutingStents, Medical Device Technology (2006),http://www.devicelink.com/mdt/archive/06/11/004.html; Dhanikula et al.,Development and Characterization of Biodegradable Chitosan Films forLocal Delivery of Paclitaxel, The AAPS Journal, 6 (3) Article 27 (2004),http://www.aapsj.org/view.asp?art=aapsj060327; and Kothwala et al.,Paclitaxel Drug Delivery from Cardiovascular Stent, Trends inBiomaterials & Artificial Organs, Vol. 19(2), 88-92 (2006),http://medind.nic.in/taa/t06/i1/taat06i1p88.pdf.

After the film is coated using a given coating method, the film can begiven time to dry. Once dried, the lased, coated stent component(s) canbe separated from the remainder of the film. Care should be taken to notdisturb the surfaces of the coated stent component(s) when beingdetached from the film and assembled or knitted together to form athree-dimensional cylindrical stent.

In another variation the therapeutic agent can be delivered by means ofa non-polymer coating. In other embodiments of the stent, thetherapeutic agent can be delivered from at least one region or onesurface of the stent. The therapeutic agent can be chemically bonded tothe polymer or carrier used for delivery of the therapeutic from atleast one portion of the stent and/or the therapeutic can be chemicallybonded to the polymer that can comprise at least one portion of thestent body. In some embodiments, a polymer can be used as a component ofthe coating formulation. Accordingly, the coating can essentially bonddirectly to a clean lased film and/or stent component, which can also becomprised of a polymer. Such an embodiment of the method can provide fora seamless interface between the coating and the lased film and/or stentcomponent. Further, in another embodiment, more than one therapeuticagent can be delivered.

The amount of the therapeutic agent can be preferably sufficient toinhibit restenosis or thrombosis or to affect some other state of thestented tissue, for instance, heal a vulnerable plaque, and/or preventrupture or stimulate endothelialization or limit other cell types fromproliferating and from producing and depositing extracellular matrixmolecules. The agent(s) can be selected from the group consisting ofantiproliferative agents, anti-inflammatory, anti-matrixmetalloproteinase, and lipid lowering, cholesterol modifying,anti-thrombotic and antiplatelet agents, in accordance with someembodiments. For vascular stent applications, some anti-proliferativeagents that improve vascular patency include without limitationpaclitaxel, Rapamycin, ABT-578, Biolimus A9, everolimus, dexamethasone,nitric oxide modulating molecules for endothelial function, tacrolimus,estradiol, mycophenolic acid, C6-ceramide, actinomycin-D andepothilones, and derivatives and analogs of each.

Some agents act as an antiplatelet agent, antithrombin agent, compoundsto address other pathologic events and/or vascular diseases. Varioustherapeutic agents can be classified in terms of their sites of actionin the host: agents that exert their actions extracellularly or atspecific membrane receptor sites, those that act on the plasma membrane,within the cytoplasm, and/or the nucleus.

In addition to the aforementioned, therapeutic agents can include otherpharmaceutical and/or biologic agents intended for purposes of treatingbody lumens other than arteries and/or veins). Therapeutic agents can bespecific for treating nonvascular body lumens such as digestive lumens(e.g., gastrointestinal, duodenum and esophagus, biliary ducts),respiratory lumens (e.g., tracheal and bronchial), and urinary lumens(e.g., urethra). Additionally such embodiments can be useful in lumensof other body systems such as the reproductive, endocrine, hematopoieticand/or the integumentary, musculoskeletal/orthopedic and nervous systems(including auditory and ophthalmic applications); and finally, stentembodiments with therapeutic agents can be useful for expanding anobstructed lumen and for inducing an obstruction (e.g., as in the caseof aneurysms).

Therapeutic release can occur by controlled release mechanisms,diffusion, interaction with another agent(s) delivered by intravenousinjection, aerosolization, or orally. Release can also occur byapplication of a magnetic field, an electrical field, or use ofultrasound.

Stent Surface Coatings with Functional Properties

In addition to stents that can deliver a therapeutic agent, for instancedelivery of a biological polymer on the stent such as a repellantphosphorylcholine, the stent can be coated with other bioresorbablepolymers predetermined to promote biological responses in the body lumendesired for certain clinical effectiveness. Further the coating can beused to mask (temporarily or permanently) the surface properties of thepolymer used to comprise the stent embodiment. The coating can beselected from the broad class of any biocompatible bioresorbable polymerwhich can include any one or combination of halogenated and/ornon-halogenated which can or cannot comprise any poly(alkylene glycol).These polymers can include compositional variations includinghomopolymers and heteropolymers, stereoisomers and/or a blend of suchpolymers. These polymers can include for example, but are not limitedto, polycarbonates, polyarylates, poly(ester amides), poly(amidecarbonates), trimethylene carbonate, polycaprolactone, polydioxane,polyhydroxybutyrate, poly-hydroxyvalerate, polyglycolide, polylactidesand stereoisomers and copolymers thereof, such as glycolide/lactidecopolymers. In an embodiment, the stent can be coated with a polymerthat exhibits a negative charge that repels the negatively charged redblood cells' outer membranes thereby reducing the risk of clotformation. In another embodiment, the stent can be coated with a polymerthat exhibits an affinity for cells, (e.g., endothelial cells) topromote healing. In yet another embodiment, the stent can be coated witha polymer that repels the attachment and/or proliferation of specificcells, for instance arterial fibroblasts and/or smooth muscle cells inorder to lessen restenosis and/or inflammatory cells such asmacrophages.

Described above are embodiments that can be modified with a coating toachieve functional properties that support biological responses. Suchcoatings or compositions of material with a therapeutic agent can beformed on stents or applied in the process of making a stent body viatechniques such as dipping, spray coating, cross-linking combinationsthereof, and the like, as mentioned and described above. Such coatingsor compositions of material can also serve purpose other than deliveringa therapeutic, such as to enhance stent retention on a balloon when thecoating is placed intraluminally on the stent body and/or placed overthe entire device after the stent is mounted on the balloon system tokeep the stent in a collapsed formation. Other purposes can beenvisioned by those skilled in the art when using any polymer material.

In accordance with an aspect of certain embodiments, a stent would havea coating applied that can alter the physical characteristics of thestent, such as to provide specific mechanical properties to the stent.The properties can include inter alia thickness, tensile strength, glasstransition temperature, and surface finish. The coating can bepreferably applied prior to final crimping or application of the stentto the catheter. The stent can then be applied to the catheter and thesystem can have either heat or pressure or both applied in a compressivemanner. In the process, the coating can form frangible bonds with boththe catheter and the other stent surfaces. The bonds would enable areliable method of creating stent retention and of holding the stentcrossing profile over time. The bonds would break upon the balloondeployment pressures. The coating would be a lower Tg than the substrateto ensure no changes in the substrate.

From the foregoing description, it will be appreciated that a novelapproach for expanding a lumen has been disclosed. While severalcomponents, techniques and aspects have been described with a certaindegree of particularity, it is manifest that many changes can be made inthe specific designs, constructions and methodology herein abovedescribed without departing from the spirit and scope of thisdisclosure.

The methods which are described and illustrated herein are not limitedto the sequence of acts described, nor are they necessarily limited tothe practice of all of the acts set forth. Other sequences of acts, orless than all of the acts, or simultaneous occurrence of the acts, canbe utilized in practicing embodiments.

While a number of embodiments and variations thereof have been describedin detail, other modifications and methods of using and medicalapplications for the same will be apparent to those of skill in the art.Accordingly, it should be understood that various applications,modifications, materials, and substitutions can be made of equivalentswithout departing from the unique and novel last next disclosed hereinor the scope of the claims.

References

Some of the references cited herein are listed below, the entirety ofeach one of which is hereby incorporated by reference herein:

-   -   Charles R, Sandirasegarane L, Yun J, Bourbon N, Wilson R,        Rothstein R P, et al., Ceramide-Coated Balloon Catheters Limit        Neointimal Hyperplasia after Stretch Injury in Carotid Arteries,        Circulation Research 2000; 87(4): 282-288.    -   Coroneos E, Martinez M, McKenna S, Kester M., Differential        regulation of sphingomyelinase and ceramidase activities by        growth factors and cytokines. Implications for cellular        proliferation and differentiation, J Biol. Chem. 1995; 270(40):        23305-9.    -   Coroneos E, Wang Y, Panuska J R, Templeton D J, Kester M.,        Sphingolipid metabolites differentially regulate extracellular        signal-regulated kinase and stress-activated protein kinase        cascades, Biochem J. 1996; 316 (Pt 1): 13-7.    -   Jacobs L S, Kester M., Sphingolipids as mediators of effects of        platelet-derived growth factor in vascular smooth muscle cells,        Am. J. Physiology 1993; 265 (3 Pt 1): C740-7.    -   Tanguay J F, Zidar J P, Phillips H R, 3rd, Stack RS, Current        status of biodegradable stents, Cardiol. Clin. 1994; 12(4):        699-713.    -   Nikol S, Huehns T Y, Hofling B., Molecular biology and        post-angioplasty restenosis, Atherosclerosis 1996; 123 (1-2):        17-31.    -   Buddy D. Ratner, Allan S. Hoffman, Frederick J. Schoen, And        Jack E. Lemons, Biomaterials Science An Introduction to        Materials in Medicine (Elsevier Academic Press 2004).

What is claimed is:
 1. An expandable slide and lock stent, the stentcomprising a tubular member having a circumference and a longitudinalaxis, the stent comprising: a first backbone and a second backbone, thefirst and the second backbones each having a reversing helical shape, afirst part of the shape extending in a clockwise circumferentialdirection and reversing into a second part of the shape, the second partextending in a counterclockwise circumferential direction, the first andsecond backbones extending along at least a portion of the circumferenceand along the longitudinal axis; a rail member defining proximal anddistal ends, the proximal end of the rail member being coupled to thefirst backbone, the distal end of the rail member extending from thefirst backbone in the circumferential direction, the rail memberconfigured to engage with an engagement element in the second backbone;and wherein the rail member is configured to provide one-way movement ofthe second backbone away from the first backbone such that the tubularmember can be expanded between a collapsed diameter and an expandeddiameter.
 2. The stent of claim 1, wherein the reversing helical shapecomprises a curvilinear shape.
 3. The stent of claim 1, wherein thereversing helical shape comprises a sinusoidal shape.
 4. The stent ofclaim 1, wherein the reversing helical shape comprises at least oneportion having a positively trending slope and at least one portionhaving a negatively trending slope.
 5. The stent of claim 4, wherein atleast one of the portions having a positively trending slope and anegatively trending slope further comprises a plurality of generallysinusoidal wave forms.
 6. The stent of claim 5, wherein the plurality ofwaves comprise a plurality of continuous curves.
 7. The stent of claim1, wherein the reversing helical shape of the first and second backbonescomprises a sub-pattern wave form extending at least partially along atleast one of the first and second backbones.
 8. The stent of claim 7,wherein the second backbone comprising a plurality of engagementelements each defined by a respective pair of sidewalls, wherein atleast one of the engagement elements defines an engagement element anglebetween about 0 degrees and about 60 degrees, the engagement elementangle being measured between a line connecting midpoints of thesidewalls of the at least one engagement element and a line parallelwith the longitudinal axis.
 9. The stent of claim 8, wherein the atleast one of the engagement elements comprises a slot.
 10. The stent ofclaim 1, wherein an intersection of the rail member and the secondbackbone is at an oblique angle.
 11. The stent of claim 1, furthercomprising second and third rail members defining proximal and distalends, the proximal end of each of the second and third rail membersbeing coupled to the first backbone, the distal end of each of thesecond and third rail members extending from the first backbone in thecircumferential direction and configured to intersect and pass throughone of a plurality of slots in the second backbone.
 12. The stent ofclaim 11, wherein one or more of the slots in the second backbone definea slot angle, wherein the slot angle extends skew relative to thelongitudinal axis.
 13. The stent of claim 12, wherein each of the slotsis disposed at a different angle with respect to the longitudinal axiscompared to the slots that are adjacent.
 14. The stent of claim 1,wherein the first and second backbones are reversing helical backbonesdefining a generally curvilinear sub-form extending along the backbonesbetween a peak and a valley of the reversing helical backbones.
 15. Thestent of claim 1, wherein the rail member comprises one or more teethfor engaging the slot to provide one-way expansion of the stent.
 16. Thestent of claim 15, wherein the slot comprises a central passage and atleast one internal recess for engaging the teeth of the rail member. 17.A method for forming the stent of claim 16, comprising forming thecentral passage as a first through hole in the backbone in acircumferential direction of stent, and forming the at least oneinternal recess as a second through hole in the backbone in a directiontransverse to the circumferential direction of the central passage suchthat the first and second through holes partially overlap.
 18. Anexpandable slide and lock stent, the stent comprising a tubular memberhaving a circumference and a longitudinal axis, the stent comprising: afirst backbone and a second backbone, the first and the second backboneseach having a reversing helical shape in which a part of the shapespirals in a clockwise circumferential direction and another part of theshape spirals in a counterclockwise circumferential direction, the firstand second backbones extending along at least a portion of thecircumference and along the longitudinal axis; wherein the reversinghelical shape of the first and second backbones each comprise a firstwave having a first frequency, a first amplitude, a first portion with apositively trending slope, and a second portion with a negativelytrending slope; wherein at least one of the first and second portionscomprise a plurality of second waves having a second frequency and asecond amplitude, the second frequency being greater than the firstfrequency and the second amplitude being less than the first amplitude;and a rail member defining proximal and distal ends, the proximal end ofthe rail member being coupled to the first backbone, the distal end ofthe rail member extending from the first backbone in the circumferentialdirection, the rail member configured to engage with an engagementelement in the second backbone; wherein the rail member is configured toprovide one-way movement of the second backbone away from the firstbackbone such that the tubular member can be expanded between acollapsed diameter and an expanded diameter.
 19. The stent of claim 18,wherein each of the waves in the plurality of second waves are generallyidentical.
 20. The stent of claim 18, wherein each of the first andsecond portions comprise the plurality of second waves.
 21. The stent ofclaim 18, wherein the second backbone comprising a plurality ofengagement elements each defined by a respective pair of sidewalls,wherein at least one of the engagement elements defines an engagementelement angle between about 0 degrees and about 60 degrees, theengagement element angle being measured between a line connectingmidpoints of the sidewalls of the at least one engagement element and aline parallel with the longitudinal axis.
 22. An expandable slide andlock stent, the stent comprising a tubular member having a circumferenceand a longitudinal axis, the stent comprising: a first backbone and asecond backbone, the first and the second backbones each having areversing helical shape, wherein the shape alternatingly reverses from aclockwise circumferential direction to a counterclockwisecircumferential direction, and comprising at least one portion having apositively trending slope and at least one portion having a negativelytrending slope, the first and second backbones extending along at leasta portion of the circumference and along the longitudinal axis; whereinat least one of the portions having a positively trending slope and anegatively trending slope further comprises a plurality of wave forms;wherein each of the portions further comprises a plurality of slots,each of the slots being disposed at a different angle with respect tothe longitudinal axis compared to the slots that are adjacent on thesame portion; and a rail member defining proximal and distal ends, theproximal end of the rail member being coupled to the first backbone, thedistal end of the rail member extending from the first backbone in thecircumferential direction, the rail member configured to engage with anengagement element in the second backbone; wherein the rail member isconfigured to provide one-way movement of the second backbone away fromthe first backbone such that the tubular member can be expanded betweena collapsed diameter and an expanded diameter.